Consequentialism is the class of normative ethical theories holding that the consequences of one's conduct are the ultimate basis for any judgement about the rightness of that conduct. Thus, from a consequentialist standpoint, a morally right act (or omission) is one that will produce a good outcome, or consequence.
Consequentialism is usually distinguished from deontology, in that deontology derives the rightness or wrongness of one's conduct from the character of the behaviour itself rather than the outcomes of the conduct. However, some argue that consequentialist and deontological theories are not necessarily mutually exclusive. For example, T.M. Scanlon advances the idea that human rights, which are commonly considered a "deontological" concept, can only be justified with reference to the consequences of having those rights. Similarly, Robert Nozick argues for a theory that is mostly consequentialist, but incorporates inviolable "side-constraints" which restrict the sort of actions agents are permitted to do. It is also distinguished from virtue ethics, which focuses on the character of the agent rather than on the nature or consequences of the act (or omission) itself. It is also distinguished from pragmatic ethics which treats morality like science: advancing socially over the course of many lifetimes, such that any moral criterion is subject to revision.
The difference between these four approaches to morality tends to lie more in the way moral dilemmas are approached than in the moral conclusions reached. For example, a consequentialist may argue that lying is wrong because of the negative consequences produced by lying—though a consequentialist may allow that certain foreseeable consequences might make lying acceptable. A deontologist might argue that lying is always wrong, regardless of any potential "good" that might come from lying. A virtue ethicist would focus less on lying in any particular instance and instead consider what a decision to tell a lie or not tell a lie said about one's character and moral behavior. An ethical pragmatist would say that, because moral progress has seemed to converge for a variety of reasons (some of which may be beyond our current awareness) against lying, it is currently reasonable to treat lying as wrong (at least until we have good reason to think otherwise).