A sapling is a small plant that resembles a tree with no leaves. This plant will never grow into an actual tree but it is one of the most important plants in the game. These plants are very nearly your sole source of Twigs which are used for all manner simple tools and traps.
This plant can be found in most Biomes. If the player has a shovel then the original plant can be dug up (even if it has been picked) and placed in the inventory. From there, the player can replant the sapling in a new location such as a settlement where it will continue to regrow over time. This allows you to make a small farm of these very important plants.