Modals are words that express different degrees of necessity, ability, possibility, and permission. They are commonly used in English grammar to modify the meaning of verbs and indicate the speaker's attitude towards the action. Some synonyms for modals include auxiliary verbs, helping verbs, modal auxiliaries, and modal verbs. These terms are used interchangeably to refer to words like can, shall, will, must, should, would, may, and might. Modals are important in English communication as they add more precision and clarity to the intended message. By using synonyms for modals, speakers and writers can create a more diverse and engaging conversation with their audience.