Plain English Meaning
A set of FAA rules that say what a piece of GPS equipment must be able to do before it can be installed in an aircraft. Equipment that meets TSO-C146 is the more capable kind of GPS — it uses extra signals that make it accurate enough to fly precision-style approaches.
Full Definition
An FAA Technical Standard Order that specifies the minimum performance standards for stand-alone GPS/WAAS navigation equipment installed in aircraft. Equipment certified under TSO-C146 uses GPS signals augmented by the Wide Area Augmentation System (WAAS) to provide more accurate, reliable position information than basic GPS alone, and supports approach operations down to LPV and LNAV/VNAV minima. For planning, an aircraft equipped with TSO-C146 navigation equipment may use that equipment to satisfy the requirement under described in the .