Thinning is in forestry a type of selective cutting primarily undertaken to make the forest more profitable in an upcoming final felling . Most of the harvest in thinnings is pulpwood as only mature trees are suitable for timber.

In agriculture and gardening, thinning is the selective removal of seedlings or young plants to allow adequate space for the remaining plants to grow efficiently. In large-scale farming, techniques like precision seeding and transplanting can eliminate the need for thinning by starting plants at their optimum spacing. On a smaller scale, such as a home vegetable garden, thinning can be used as a way to make maximum use of space for certain crops. For example, beets, carrots, green onions and others can be planted densely, and then thinned to make room for continued growth, and also as a harvest of baby vegetables (beet greens, baby carrots, baby onions).