Biennium

A biennium is a period of two years. The term is commonly used in government, budgeting, and legislative contexts to describe a two-year cycle, such as a biennial budget period or legislative session cycle. Its plural can be written as bienniums or biennia, although “biennia” is common in formal usage.

A biennium lasts two years. The exact start and end dates depend on the context in which the period is defined. For example, a state budget biennium may cover two fiscal years rather than two calendar years, so the relevant government or organization sets the dates for a particular biennial period.

A biennium is the two-year period itself, while biennial is usually an adjective meaning occurring every two years or lasting two years. For example, a legislature may operate within a biennium and publish a biennial budget. The words are related but are not grammatically interchangeable in a sentence.