Plain English Meaning
On some approaches, you find the point where you must go around by starting a timer when you cross a specific fix and flying for the published number of minutes and seconds. When the time runs out, if you can't see the runway, you go missed.
Full Definition
A method used on certain non-precision instrument approaches to determine the missed approach point (MAP) by starting a stopwatch when crossing the final approach fix (FAF) inbound and flying at the published groundspeed-corrected time until the MAP is reached. When the published time elapses and the runway environment is not in sight, the missed approach must be initiated.