It can refer to any event which happens yearly.
It can refer to a plant with a lifespan of a year or less. These are generally plants adapted to life as weeds or in difficult habitats where quick flowering and seeding are necessary.
It can refer to a publication, a book or a magazine, comic book or comic strip which comes out yearly. If it is not a book or a comic, it may be brought out to praise some celebrity or celebrities, or even a holiday camp (such as the Butlins annual).
List of collectable annuals: