An annual, like Pansies and Petunias, is a plant that lives and dies in one growing season, whereas a perennial, such as Lantana, re-grow year after year.
Perennials grow slowly the first season they are installed, require less care, and do not experience insect problems like annuals. On the other hand, annuals have a much broader color selection. Mixing both types of plants in your landscape is always a great idea!