Scientology seems at time to have its own distinct language, rich with unique terms and acronyms.  In many cases the words are common (ethics, clear) but they’ve been “loaded” or given new definitions within Scientology.

In fact it’s a documented cult tactic to immerse members into its own jargon.  This “Language Loading” helps isolate members from the outside world and can be considered a form of mind control.

This is a glossary of the most common Scientology terms taken from Xenu-Directory.net.  Their site has a complete list of definition for Scientology terms and when linked they have more information on the subject.

AD - After Dianetics. Used on issues such as HCOBs and HCOPLs (Hubbard Communication Office Bulletins and Policy Letters) to show the year. It is based on the Christian calendar, but with a base year of 1950 with the release of Hubbard's book "Dianetics"; thus AD 15 = anno Domini 1965.

Auditing - The action of running Scientology or Dianetic processes on a PC (a preclear; someone receiving Scientology processing). Auditing usually involves a Meter, with the PC holding onto the soup cans electrodes, and the Auditor taking down notes and asking questions.

Blow - To leave Scientology suddenly. Also, the person who does this. "Sam Blew off post today; he's our third Blow this week!"

Bridge - The bridge to total freedom; the list of auditing actions needed to get to the highest OT (operating thetan) level, currently OT 8. The Bridge costs roughly $300,000 US, and is depicted on the Gradation Chart of Human Awareness and Abilities. L. Ron Hubbard's "Bridge to total freedom" has two sides. One is auditor or therapist training classes or classifications, the other is receiving auditing or "therapy" such as Grades and OT levels, qv. At the lower levels the grades and classes or classifications correspond, this pretty much stops after Class 6 (Saint Hill Special Briefing Course).

BT (Body Thetan) -  Usually plural. Evil spirits which need to be exorcized. "OT 5 consists entirely of running out BTs; what a bore."

CCHR - The newspeak-named Citizen's Commission on Human Rights, run by a Scientologist by the name of Dennis Clarke. CCHR's main purpose is clearing away the "Psyches" (mental health professionals; seen by Scientology as evil aliens from the fifth galactic invader force) to make way for Scientology's advance into society. CCHR is a front group for Scientology.

Clear - A person audited enough to be free of the "bank," or reactive mind. (The sum of the memories of pain and unconsciousness the person has) A low-level superman-type person; a baby OT (Operating Thetan). "Samantha just had her Clear Certainty Rundown, and is now considered a clear!"

David Miscavige (DM) – The current leader of Scientology. He took over after Hubbard died.

Declaring - The act of blacklisting within the cult; the result is an "SP" (Suppressive Person, someone who does not like Scientology) who can be "Sued, tricked, lied to, or destroyed" as per the cult's policy. "Eric was declared Suppressive at his Comm Ev."

Disconnection - The act of severing ties with family, friends, and loved ones that the cult often forces its victims to do when these same loved ones are declared SPs, Suppressive Persons, (often for expressing doubts about the victim's involvement in the cult) which the victim then supposedly becomes PTS, a Potential Trouble Source for Scientology, to. "I was ordered to disconnect from my wife after she was declared." See SP, PTS.

Enturbulated - Hubbardese for being upset. "Suzy found ars so enturbulating, she ran away."

Ethics – 1. A section of a Scientology Org (organization) that keeps people in line, and the Hubbardian policy that deals with it. "Keep your nose clean, or I'll route you to Ethics, Mr.!"

2. Ethics actually consist, as we can define them now in Dianetics, of rationality toward the highest level of survival for the individual, the future race, the group, and mankind, and the other dynamics taken collectively. The highest ethic level would be long-term survival concepts with minimal destruction, along any of the dynamics.

Fair Game – Scientology’s way to deal with Suppressive Persons. They may be “sued, tricked, lied to, or destroyed”

Flag Base (Flag) – A near top level Scientology Org set up in Clearwater.

Freeloader debt - A debt incurred by staff members who break their 3, 5, or one billion year (in the Sea Org) contracts, and are thus required to pay for every auditing action and training course done to them while on staff. The freeloader debt usually runs into the tens of thousands, but cannot be collected in most cases as the contract in not considered to be in good faith.

Freewinds - The Sea Org ship that cruises around tropical ports and gives the OT8s (top level Scientologists) a hangout while they proceed with their auditing.

Handle - To fix something up or solve a problem. "Helena Kobrin and Elaine Siegel were assigned to handle the situation in ars."

Illegal PC - A Preclear who cannot be audited by virtue of actually needing some kind of help. Auditing is only for the able, or people who don't need help, as per policy; it is for making the able more able, or bilking them for more money. This paradox is explained by the fact that people who actually need help are harder to turn a profit on. Specifically, an Illegal PC is one who has had psychiatric treatments in the past, or appears to Scientologists like they have (a streetperson or prostitute, for example) and is deemed too damaged to touch, and a serious security risk to boot. "Jack Farmer is an Illegal PC; he may not receive the next auditing level he needs and wants."

Introspection Rundown (IRD) - A therapy for handling psychotic breaks in the cult. Involves locking the person up to prevent bad PR with the isolation step, also called "baby watch". Sometimes instilling such wacky ideas as Xenu, Body Thetans and OT III can make people a bit unstable; the IRD is used to contain people when they flip out.

LRH – Lafayette Ron Hubbard (L Ron Hubbard), the creator of Scientology

MEST - Matter, Energy, Space, and Time; the constituents of the physical universe, or the physical universe itself. Seen as a lesser domain than the spiritual or Theta realm.

OSA - Office of Special Affairs. The "dirty work" department, the cult's KGB. Took over from the Guardian's Office, when the GO's leaders went to jail for infiltrating government offices.

OT (Operating Thetan) - The exalted state that is the target of Scn's weird "technology" of removing body thetans, said to be accompanied by strange powers like the ability to kill someone with a thought or fry a bug at a considerable distance. See OT.

Operating Thetan, one who is above Clear, a state of partial enlightenment, and who is not just free of unconscious impulses, but is free of other things too so that they can operate, and be causative over the physical universe and do kewl things like fry bugs, read minds, kill people with a thought, etc.

Note: most of the OT levels have been modified over time, sometimes extensively. These modifications are designated "New OT (level)".

Office of special affairs (OSA) - Office of special affairs. The "dirty work" department, the cult's KGB. Took over from the GO, Guardian's Office, when the GO's leaders went to jail for infiltrating government offices, stealing and altering official files that put the cult in a bad light.

Potential Trouble Source  (PTS) - Potential Trouble Source. Someone who is in contact with an SP, a Suppressive or anti-Scientology person, and therefore may cause trouble for the cult. "Mary is a PTS Type III." Adjective; "She is PTS to that Wholetrack SP on her lines." See also individual types of PTS - 1 to 3, and A to J, SP, Disconnection.

RTC (Religious Technology Center) – The branch of Scientology that holds the cult’s copyrights and trademarks.

Rehabilitation Project Force (RPF) - The cult's internal gulag where bad people are sent for punishment or "rehabilitation"; a brain washing and penal organization.

Sea Org (Organization) – The highest-ranking members of Scientology staff. They form most of the central management of the cult.

Sec Checking, Security Checking - Security Checking. Running lists of questions on a PC or patient using the Meter to find criminal behavior that can be used as potential blackmail, should the PC ever blow or become critical of the cult. Similar to a confessional; the PC is lied to and told the revealed secrets and overts will remain confidential, yet the cult often publishes and distributes the items found by Sec Checking, which are written down in folders at the time of the session. Term comes from Hubbard's extreme paranoia about Communist, governmental, or psychiatric infiltration of Scientology, and the need to run Security checks on new Scientologists.

Snow White - The code name for a cult espionage operation. Snow White's goal was to infiltrate government offices and purge their files of incriminating material that made the cult look bad.

Squirreling – subverting the original Hubbard texts via alteration
Mary Sue Hubbard (MSH) – L Ron Hubbard’s third wife and a former high ranking member of the cult.

Suppressive Person (SP) - an evil person; someone who criticizes Scientology in any way. The two are one and the same in the cult.

Tech - Short for "technology", the quasi-scientific auditing "therapy" processes and actions of Scientology, as found in HCOBs, Hubbard Communication Office Technical Bulletins, collections of which are found in the Red Vols, qv. "You are hereby declared an SP, Sam, for committing Out-Tech."

Touch Assist - A cult medical regimen meant to reduce ridges (afflicted areas due to impact) in the body due to injury. Several methods are used. One involves repeatedly touching the injured part back to the object which caused the injury. Another involves using the hands to smooth away the supposed built-up ridges or force lines from impact between objects or flows. Yet another involves sticking a finger on the body, and saying "feel my finger" repeated, as always, ad nauseum.

Withhold - After committing an Overt (undisclosed bad act), people try to hide it or Withhold it; thus a Withhold is what you're hiding. "Sit down and write up your Overts and Withholds." See MU.

Wog - A derogatory and racist term the cult co-opted from British slang, and now uses to refer to people outside of Scientology's purview.

Xenu - the evil galactic ruler that packaged us all up, put us on Hawaii, and blew us up with H bombs 75,000,000 years ago, according to L. Ron Hubbard, author of Dianetics.