What is perennial? What is perennial? Lasting or active through the year or through many years.Lasting an indefinitely long time; enduring: perennial happiness. Appearing again and again; recurrent. See Synonyms at continual.Botany Living three or more years.Botany A perennial plant.Something that recurs or seems to recur on a yearly or continual basis: "that hardy perennial, the budget deficit” ( David S. Broder).