Shrubs are bushes. Unlike trees, shrubs have multiple stems and are shorter - usually under 5-6m tall. A large number of plants can be grown as shrubs or trees, depending on the growing conditions.
Horticulturally, shrubs are usually broad-leaved plants, although smaller conifers (e.g. Common Juniper) can be grown with a shrub shape and structure.
Botany and ecology have stricter definitions, and ecology uses these along with foliage cover to define different kinds of landscape (e.g. "open-scrub", "low shrubland");
Use this tag for general questions about shrubs, shrubberies, and choosing shrubs for a particular location. Species/variety specific questions should use the specific plant tags instead.