A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m (15–20 ft) tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience. Small, low shrubs such as lavender, periwinkle and thyme are often termed subshrubs.

An area of cultivated shrubs in a park or garden is known as a shrubbery. When clipped as topiary, shrubs generally have dense foliage and many small leafy branches growing close together. Many shrubs respond well to renewal pruning, in which hard cutting back to a 'stool' results in long new stems known as "canes". Other shrubs respond better to selective pruning to reveal their structure and character.

Shrubs in common garden practice are generally broad-leaved plants, though some smaller conifers such as Mountain Pine and Common Juniper are also shrubby in structure. Shrubs can be either deciduous or evergreen.