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), have to, have got to, had better, used to, dare, need, going to. These have some but not all properties of full modal verbs of them.