MAASP In Drilling Definition, Calculations For Well Control
During well control operations the maximum allowable borehole fluid pressure at the casing shoe is normally considered to be the critical factor, based on the assumption that the weakest formation is at the shoe. For prac­tical purposes, the corresponding pressure at the surface (Drilling MAASP or Maximum allowable annular surface pressure) is calculated through specific formulas and used during well control operations.
https://www.drillingmanual.com/maasp-maximum-allowable-annular-surface-pressure/