It is a decorated rectangular silver, brass, ceramic, olive wood or stone box that Jews attach to the doorpost of their house and gates.
“And you shall write them upon the doorposts of your house, and upon your gates.”
The box contains parchment inscribed with biblical verses from the Shm’a (“Hear O Israel, the Lord Our God, the Lord is One”) prayer in Deuteronomy 6.
On the outside of the box is inscribed either the first letter (shin), or all the Hebrew letters of Shaddai, the name which the Lord revealed to Abraham when he offered His covenant. (Genesis 17)
Look for a mezuzah on the door to your hotel room. You will find a wide selection of mezuzahs in nearly every Jewish gift shop.