Calando is the opposite of accelerando, which indicates a gradual increase in both tempo and volume.
When a piece of music is marked with the term "calando," the musicians should play it with a sense of gradual relaxation. The tempo should become slower and the dynamics should decrease until they reach a soft and gentle ending.
Calando can be used to create a sense of anticipation, suspense, or calm. It is often used at the end of a piece of music to create a sense of conclusion.