BFR - Biennial Flight Review.
Long before JAA introduced the 'one hour with an instructor' the Americans had a similar system. In order to fly as PiC you must have had a flight with an instructor (BFR) within the preceeding 24 calendar months.
Don't worry about it - Rainbow aren't going to send you off in one of their aircraft without a checkout, which will, in effect, be your BFR.