A sentence is a group of words giving a complete thought. A sentence must contain a subject and a verb (although one may be implied). For example: The cat sat on the mat. (Here, the subject is "the cat" and the verb is "sat." The words convey a complete thought.

a group of words, usually containing a verb, that expresses a thought in the form of a statement, question, instruction, or exclamation and starts with a capital letter when written: He's very impatient and always interrupts me mid-sentence. Your conclusion is good, but the final sentence is too long and complicated.