The Latin phrase that ends a Catholic mass.
The translation is not unambiguous. When mass is held in English it is ended with something like "Go, mass has ended." However, the latin word "missa" came to mean mass for the very reason that it is used in this phrase. The other - older - meaning of the word is that it is a form of the verb "mitto", to send (as in eg the English word mission). There are several suggestions to what the phrase originally ment, but probably it was along the lines of "Go, it is the dismissal".
Mass is actually not always ended with the words "Ite missa est", eg requiems are ended with "Requiescant in pace".