(quoting from various sources):

Compost is the product of a planned, controlled process of making decomposed material as an organic fertiliser.

A mixture of decayed organic matter, as from leaves and manure, used to improve soil structure and provide nutrients.

Composting is a natural biological process where bacteria, fungi and other organisms decompose organic materials such as leaves, grass clippings, and food wastes. The end product is called compost. While composting occurs naturally, the process can be accelerated and improved by human intervention.