A shrub is a small-to-medium-sized perennial woody plant with persistent woody stems above the ground. Unlike herbaceous plants, shrubs have multiple stems and can be either deciduous or evergreen. In horticulture, the term "bush" is used to describe the shape of a plant, while "shrub" is defined as a plant that retains structure above ground year-round and cannot be split or divided because the growth is coming from one set of roots. Shrubs can be as small as a dwarf cotoneaster or as tall as a lilac. The terms "shrub" and "bush" are often used interchangeably, but a hedge is defined as a fence or boundary formed by closely growing bushes or shrubs.