A mezuza (pl., mezuzot) is a small, sofer-inscribed parchment scroll containing the two Torah paragraphs commanding us to put mezuzot on our doorposts and gates: Deuteronomy/Devarim 6:4-9 and 11:13-21 (these are the first two paragraphs of the shema prayer.)  Each doorway that is related to where people live must have a mezuza.

Mezuzot are placed on the right side of doorways as you enter in apartments, buildings, or even recreational vehicles that you rent for 30 days or more (or that you purchase/own), in which you sleep.

A mezuza has protective value in that it reminds us to think about God each time we walk past a doorway or gateway, and so the particular name of God written on the mezuza (shin-daled-yud) likewise can serve as an acronym for God’s role as “Shomer dirot Yisrael”—Watcher over the dwelling places of Israel.