"Auditing", sometimes called "processing", is intended to help a person resolve difficulties or to gain abilities.
Most auditing is done with the assistance of another person who is an "auditor". For operating thetan levels 1, 2, 3, 7, and 8 a person is said to "solo audit". When solo auditing, the person being audited is a "solo auditor", after having done adequate training on how to do so.
Regardless of whether a person is auditing solo or being audited by another, a Case Supervisor (CS) decides what processes are run on the person being audited and writes a "program" for the person. This is called "CSing" a case. Though specific matters can be addressed in auditing, it is hoped a case program ultimately results in a person moving up "The Bridge".
"Self-auditing" is an expression which implies someone is thinking about things rather than running processes which have been planned by a Case Supervisor.