shelter in place

or shel·ter-in-place

[ shel-ter in pleys ]
/ ˈʃɛl tər ɪn ˈpleɪs /

noun

an official order, issued during an emergency, that directs people to stay in the indoor place or building that they already occupy and not to leave unless absolutely necessary.

verb (used without object)

to stay in a safe indoor place or building during an emergency: If police believe there is an active shooter on campus, they will order students and faculty to shelter in place.