Definition: A biennial is a plant that requires two growing seasons to complete its life cycle. During the first growing season it produces mainly foliage. In it's second year it will flower and set seed, often early in the season. Parsley is a biennial that goes to seed in the spring and becomes less valuable as a culinary plant. Some biennials, like hollyhocks, self seed and appear to be perennial.
Examples:I don't mind biennials dying after their second year, as long as they self-seed.