Plain English Meaning
How recently you have actually flown the kind of flying you are about to do. The rules require you to have done certain tasks recently enough that your skills are still sharp and legally current.
Full Definition
A regulatory and practical concept referring to how recently a pilot has performed specific flight operations, used to determine whether the pilot is currently qualified and proficient to act as pilot in command under given conditions. For instrument flying, FAR 61.57 sets minimum recent experience requirements -- such as having performed, within the preceding six calendar months, a specified number of instrument approaches, holding procedures, and intercepting and tracking courses using navigation systems.