In botany, trunk (or bole) refers to the main wooden axis of a tree that supports the branches and is directly attached to and supported by the roots. The trunk is covered by the bark, which is an important diagnostic feature in tree identification, and which often differs markedly from the bottom of the trunk to the top, depending on the species. The trunk is the most important part of the tree for timber production. Trunks occur both in "true" woody plants as well as non-woody plants such as palms and other monocots though the internal physiology is different in each case. In all plants, trunks thicken over time due to formation of secondary growth (pseudo-secondary growth in monocots).

Trunks can be vulnerable to damage, including sunburn.