Biennial means happening once every two years. A biennial celebration occurs in 2020, then again in 2022, then 2024, and so on. Many cities host biennial art festivals or exhibitions, giving artists time to create new work between events.

The word also describes plants that complete their life cycle in two years. A biennial plant grows leaves and roots in its first year, then flowers, produces seeds, and dies in its second year. Carrots, parsley, and foxgloves are common biennial plants. Gardeners need to know which plants are biennial because they won't see flowers or vegetables until the second growing season.

Be careful not to confuse biennial with biannual, which means twice per year. If something happens biannually, it occurs two times within the same year. If it happens biennially, it occurs once every two years. That's a big difference: a biannual meeting happens every six months, while a biennial meeting happens every twenty-four months.