Botanically speaking, an annual is a plant
that goes from seed to seed in one season and then dies. True
annuals cannot be taken inside for the winter.
In the gardening world, the
term "annual" is used to designate any plant
that is grown for one season and then
dies at frost in the temperate regions of
the world. In this case, the term also
includes plants such as
(geraniums), coleus and
impatiens which are,
botanically, perennials in that they
normally live more than two years in nature.
They are used as annuals since they are not
winter hardy in the colder climates.
To make things even more
confusing, we have the term "bedding plants"
which will include tropical plants,
vegetable seedlings and "annuals" discussed
above. Stranger, to me anyway, is the
term "half-hardy" perennials which you see
in British books. It seems to me that tender
perennials is a better choice.
Below is an index of plants
commonly grown as annuals (of course some
are perennials in warm
climates) in the home landscape: