Even those brand-new to gardening usually know the difference between annual and perennial plants:
Annual: a plant that lives and dies in one growing season
Perennial: a plant that regrows year after year
It’s a straightforward distinction, except when it’s not.
For instance, some annuals re-seed themselves. Meaning that, though they die, they leave seed behind that germinates the next year. They might move around, but they do come back in our gardens. Cosmos sometimes do this in my garden.
Second, some perennials are short-lived. They won’t return to our gardens forever but maybe only for a few years. If you love a short-lived perennial, it’s a good idea to save seed or take cuttings in order to keep these plants growing in your space. Verbascum (‘Southern Charm’ Verbascum is a favorite in my garden) is short-lived, but it is easy to start new plants from seed.
And finally, some plants are perennials in certain climates (the warm southern United States, for instance) but northern gardeners can still grow them as annuals. Meaning, the winter cold will keep them from re-growing the following year.
Here are a few other related concepts:
Biennial: These plants complete their lifecycle over two years.
Herbaceous Perennial: unlike woody shrubs and trees, these perennials die back completely to the ground before regrowing the following year (for example, roses are a shrub but peonies are an herbaceous perennial)