Plain English Meaning

The altitude you must be at -- and no lower than -- when you join the descending beam that guides you down to the runway on an instrument approach.

Full Definition

The minimum altitude, published on an instrument approach chart, at which an aircraft must be established before intercepting the glideslope (for an ILS) or glidepath (for an LPV, LNAV/VNAV, or similar vertically guided approach) inbound to the runway. It is depicted on the profile view of the approach chart, typically by a lightning-bolt symbol at the final approach fix, and represents the altitude at which the is joined for the .