The term finite is applied to a verb (phrase) which takes a subject ([you] sang), can show contrasts in tense ([you] sing/sang) and in agreement ([you] sing/[he] sings) and which can occur alone in an independent sentence or main clause:

[they] sing [they] have sung [they] are singing [they] are sung [they] have been singing [they] have been sung

The non-finite parts of the verb are the infinitive (to sing), the present participle (singing) and the past participle (sung).