Flag stands for "Flag Land Base" and refers to two buildings in Clearwater, Fl. The first, formerly the New Fort Harrison Hotel, was purchased by the Church in 1975 and served as the religion's second headquarters for the church after Hubbard was forced to abandon Saint Hill in Susex, England to avoid international extradition for fraud.

Fort Harrison is connected to the Flag Building via a skybridge, and the complex is used largely as a training center for parishioners studying higher level OT (Operating Thetan) courses.

Ex members also said Flag was the location where Sea Org members accused of "serious deviations" were sent to perform forced labor in the Rehabilitation Project Force (RPF). 

Many members who leave the Sea Org are charged with a "freeloader's debt," and the RPF is where they're sent to work off the tens and hundreds of thousands the church says they owe for their room, board, and training during their time in Sea Org — even though the actual wages they receive in Sea Org are almost nothing.