That point in an instrument approach procedure at or before which the prescribed missed approach procedure must be initiated in order to ensure that the minimum obstacle clearance is not infringed.
Source: ICAO Doc 8168 PANS-OPS
The missed approach procedure is constructed in such a way as to provide prescribed obstacle clearance, and separation from other procedural traffic, within a portion of the airspace. It is initiated in case the required visual references have not been obtained and includes two elements - a climb and a horizontal manoeuvre (which may include a turn or simply require the aircraft to continue on the runway heading).
Normally, the crew must follow the published missed approach procedure unless other factors (such as an instruction by the air traffic controller or other safety concerns) have greater priority.
The climb portion must be initiated at or above the MDA/H and, depending on the circumstances, may start before the MAPt. The horizontal manoeuvre (the turn) however, is handled differently. If the decision to go around is made prior to the defined missed approach point (MAPt), the aircraft must continue the lateral tracking of the approach being conducted and only initiate the turn after passing that point. Doing otherwise could result in insufficient terrain clearance or a CFIT. If the decision to execute a missed approach is made at the MAPt, the missed approach procedure (including the turn) is to be initiated immediately.