A plant which naturally completes its life
cycle within one year. The life cycle includes germination of seed,
growth to maturity (which may or may not include flowering),
production of seed and then dieing.
Some plants (such as tomatoes) are grown as if they are annuals but
are in fact perennials or biennials. The normal reason for growing
them as annuals is that they are not hardy and will be killed by
cold weather conditions in some countries.