Terete is a term used in botany to describe a cross section that is circular, or like a distorted circle, with a single surface wrapping around it. This is usually contasted with cross-sections that are flattened, with a distinct upper surface that is different from the lower surface. The cross-section of a branch in a tree is somewhat round, so the branch is terete. The cross section of a leaf has an upper surface, and a lower surface, so the leaf is not terete. Fruticose lichens are terete, with a roughly circular cross section and a single wrap-around skin-like surface called the cortex, compared to foliose lichens and crustose lichens, which have a flattened cross section with an upper surface that is distinct from the lower surface.
The Collaborative International Dictionary
[L. teres, -etis, rounded off, properly, rubbed off, fr. terere to ru
] Cylindrical and slightly tapering; columnar, as some stems of plants.
adj. especially of plant parts; cylindrical and tapering
a. Having a smooth circular cross-section; cylindrical.