At its simplest, ethics is a system of moral principles. They affect how people make decisions and lead their lives.
Ethics is concerned with what is good for individuals and society and is also described as moral philosophy.
Ethical egoism claims that it is necessary and sufficient for an action to be morally right that it maximize one's self-interest. (There are possibilities other than maximization. One might, for example, claim that one ought to achieve a certain level of welfare, but that there is no requirement to achieve more. Ethical egoism might also apply to things other than acts, such as rules or character traits. Since these variants are uncommon, and the arguments for and against them are largely the same as those concerning the standard version, we set them aside.)