A true annual is a plant that completes its life cycle in one year. This means it goes from seed to flower and back to seed and then dies off, during the course of one growing season.
The entire mission of an annual plant is to produce seed to ensure the propagation of future generations.
A perennial plant or simply perennial is a plant that lives for more than two years. The term (per- + -ennial, "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widely used to distinguish plants with little or no woody growth from trees and shrubs, which are also technically perennials.
Perennials, especially small flowering plants, that grow and bloom over the spring and summer, die back every autumn and winter, and then return in the spring from their rootstock, are known as herbaceous perennials. However, depending on the rigors of local climate, a plant that is a perennial in its native habitat, or in a milder garden, may be treated by a gardener as an annual and planted out every year, from seed, from cuttings or from divisions. Tomato vines, for example, live several years in their natural tropical/subtropical habitat but are grown as annuals in temperate regions because they don't survive the winter.