Posted: 25/03/2017 at 13:44
Annual means that the plant will grow, flower/seed and then die in one year. It will not flower the following year. i.e. it lasts one year.
Perennial means that the plant will flower year after year. It will probably die down each winter but each following year it will grow again and flower and produce seeds. i.e. it goes on for several, sometimes many years.
Bi-ennial means that you sow the seeds and a plant grows one year, then it dies down over the winter and in the spring the plant grows into a mature plant, flowers, produces seeds and then dies. i.e. it lasts two years.
There's a more detailed explanation here http://www.edinburghgardenschool.com/2013/06/definitions-of-annual-biennial-perennial-ephemeral /
Crocuses won't produce more flowers this year, but the leaves will die down and feed the corms (bulbs) and next spring they'll flower again. With any luck the corms will have multiplied and you'll have even more flowers in following years.
Hope that helps