a word used to describe an action, state, or occurrence, and forming the main part of the predicate of a sentence, such as hear, become, happen
Verbs can appear in any one of three progressive tenses: present progressive, past progressive, and future progressive. The verbs in the progressive form use a form of "to be" + the present participle (an -ing verb). (It is the form of the helping verb that indicates the tense.)