Utilitarianism is a form of the broader ethical theory of consequentialism. Utilitarianism is an ethical theory that embodies morality. Right or wrong is determined by how much happiness or pleasure your actions bring to the people around you. If what you did makes people sad, you are wrong and vice versa.
The founder of utilitarianism, Jeremy Bentham, described it as “that property in any object, whereby it tends to produce benefit, advantage, pleasure, good, or happiness…(or) to prevent the happening of mischief, pain, evil or unhappiness to the party whose interest is considered.” This definition shows clearly why this theory falls under consequentialism.
Since this ethical theory relies on the consequences of your action on the people around you, utilitarianism is a consequentialist theory. Other forms of consequentialism are egoism and altruism. Consequentialism bases judgement on the consequences of actions rather than the action itself. This theory is a part of the broader category of teleological ethics.