Plain English Meaning
A certification level for airplanes that are built stronger than normal training airplanes and are allowed to do more aggressive maneuvers, but still not full aerobatics.
Full Definition
An FAA airworthiness certification category for airplanes intended for limited acrobatic operations, certified to withstand load factors from +4.4g to -1.76g. Aircraft in this category may be approved for maneuvers such as spins (if specifically tested), lazy eights, chandelles, and steep turns exceeding 60 degrees of bank, but are not approved for full aerobatic flight.