A pillow placed between members of the opposite sex (or of compatible sexualities) when sharing a bed for the evening. This pillow is intended to explicitly communicate the desire to abstain from sexual activity of any type, making it "safe" for platonic bed-sharing.
Same as pillow partition
, but more used for people who are in relationships and don't want to cheat -- but would totally consider it if they were single.
Male friend: You can have my bed and I'll sleep on the couch.
Female friend: Don't be silly. We'll just put a chastity pillow between us and I'll try to keep my cold feet off you.
Male friend: If you say so.