Definition of imperative:
(n) :
the
grammatical mood expressing an order (see
jussive). In English, the imperative form of a verb is the same form as that of its second person ("you") present tense; an essential action, a must: something which is imperative
"the verbs in sentences like "Do it!" and "Say what you like!" are in the imperative."
"it is imperative that you come here right now."