Trees refers to fast growing function based on Kruskal's tree theorem. It commonly describes a perennial woody plant, not exactly defined, but differentiated from a shrub by its larger size (typically over a few meters in height) or growth habit, usually having a single (or few) main axis or trunk unbranched for some distance above the ground and a head of branches and foliage, any plant that is reminiscent of the above but not classified as a tree (in any botanical sense), and an object made from a tree trunk and having multiple hooks or storage platforms, which gives the term a broader and more practical sense than a single short definition would suggest. Depending on context, it can also point to a device used to hold or stretch a shoe open, the structural frame of a saddle, and a connected graph with no cycles or, if the graph is finite, equivalently a connected graph with n vertices and n−1 edges, so the category can cover literal uses, related ideas, and more figurative extensions of the same core meaning. Taken together, these meanings present Trees as a flexible theme rather than a narrowly technical label, covering the central idea people usually mean when they use the word while still leaving room for closely related senses that appear in real language.
