A true annual is a plant that completes its life cycle in one year. This means it goes from seed to seed and then dies off, during the course of one growing season. The whole mission of an annual is to produce seed and propagate. That's why deadheading or removing spent flowers before the seed matures, produces more flowers and therefore more potential seed.
Perennial plants are the backbone of every successful landscape and garden border. They are available in a wide range of sizes, colors and blooming seasons. Perennials grow and bloom over the spring and summer and then die back every autumn and winter, then return in the spring, bigger and better with every passing season. Typically, they grow from their root stock rather than seeding themselves as an annual plant does. These 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.