An annual plant is one that completes its growing cycle -- from seed, to flowering, to producing seed -- in a single season, and must be replanted the following year. Most annuals germinate in the spring, flower in late spring and summer, and die in the autumn, but a few can germinate in late summer and autumn, remain partially dormant over the winter, then resume growth in the spring, completing their cycle in the summer. Some annuals are less hardy than others and can be killed by even light frosts and hence must be grown indoors before planting outside in the spring.
In contrast, perennials are flowering or foliage plants whose roots live from year to year. These plants grow back each spring, either from the original root, or through self-seeding. They typically don't bloom for as long as annuals, however. Some perennials are more delicate and need to stored for the winter and replanted in the spring, but in warmer climates, the root can be left in the ground for the winter.
Common perennials: clematis, meadow sage, evening primrose, black-eyed susan, coral bells, day lilies Common annuals: geraniums, impatiens, marigolds, pansies, begonias, zinnias, Mexican sunflowers