ś.p.

Świętej pamięci literally means of holy memory. It is a respectful way to say a person is dead, used much like the late or of blessed memory in English, and it is written before the name: ś.p. Jan Kowalski.

Polish dictionaries spell the abbreviation śp., but you will also see ś.p. with two periods. In a marriage or death record it tells you a parent or spouse was already dead when the entry was made. Niegdyś, formerly, is used the same way in older records.