There are specific markings for changes in tempo. The most common ones are listed here. Notice the use of the rit marking near the end of the following song.
accelerando (gradually becoming faster) | rallentando or ritardando | (gradually becoming slower) |
ritenuto (rit) (immediately slower) | a tempo | (return to the original tempo) |
The melody of this traditional Christmas song is derived from the natural minor scale. Because of this, it is said to be in a minor key. It is written here in the key of A minor.