(biennual) Flight Review (Excerpt from FAR §61.56):

No person with an american pilot license may act as pilot in command of an aircraft unless, since the beginning of the 24th calendar month before the month in which that pilot acts as pilot in command, that person has -

1. Accomplished a flight review given in an aircraft for which that pilot is rated by an authorized instructor; and
2. A logbook endorsement from an authorized instructor who gave the review certifying that the person has satisfactorily completed the review.

This flight review consists of a minimum of 1 hour of ground training and 1 hour of flight training and must include:

1. A review of the current operating and flight rules of Federal Aviation Regulations Part 91; and
2. A review of those maneuvers and procedures that, at the discretion of the person giving the review, are necessary for the pilot to demonstrate the safe exercise of the privileges of the pilot certificate.