Auditing in Scientology is a form of personal spiritual counseling. A person trained and qualified in auditing, called an auditor, listens to individuals to help them on their path to understanding. Auditor is defined as one who listens, from the Latin word audire, meaning "to hear or listen." An auditor is a minister or minister-in-training of a church of Scientology.
Auditing helps people look at their life and come closer to total spiritual understanding.
Here is a link to a video by the Church of Scientology describing auditing.