Both are correct grammar. Depends on what you mean to communicate. If we use the definite article "the" it refers to a specific group of people that share some quality. Usually that shared quality is clear from the context (but not always). If we use "people" without the definite article "the" it doesn't refer to a specific group and therefore it means all people or people in general. For example: "People want money." = "Humans want money." "The people want money." = "The citizens of the country want money."