(annual ring) A layer of wood cells added to a tree trunk or stem during one growing season.

Tree trunk rings which are used to judge age & growth.

Growth rings (or "tree rings" or "annular rings") can be seen in a horizontal cross section cut through the trunk of a tree. Visible rings result from the change in growth speed through the seasons of the year, thus one ring usually marks the passage of one year in the life of the tree. The rings are more visible in temperate zones, where the seasons differ more markedly.