This section is from the book "Harper's Guide To Wild Flowers", by Caroline A. Creevey. Also available from Amazon: Harper's Guide To Wild Flowers.
Annuals die down every year and are reproduced from seed the next season. Perennials continue to live year after year. Biennials have a life of two years, storing food for themselves the first year, upon which they live the next, dying down after that.
A leaf axil is the angle formed by the leaf and its stem, on the upper side of the leaf. Most buds spring from leaf axils.
The foregoing and a few additional technical terms are summed up in the following