Shut In Drill Pipe & Casing Pressure
After taking an influx, closing the BOP stack & shutting in the well, pressure will build up on the standpipe and casing gauges. This is because of the hydrostatic under balance (drilling fluid weight too low to balance formation pressure). The pressure on the standpipe manifold is "Shut In Drill pipe Pressure" SIDPP, and what appears on the casing gauges is called "Shut In Casing Pressure" SICP.
https://www.drillingmanual.com/shut-in-drill-pipe-casing-pressure/