A modal verb (/məʊdəl vɜ:b/) is a verb that expresses modality. In English, there are two types; full modal verbs and semi-modal verbs.
The full modal verbs are can, could, will, would, may, might, shall, should and must.
The semi-modal verbs are ought (to), had better, used to, dare, need, going to. These have some but not all properties of full modal verbs of them.