A system or set of beliefs people embrace to identify what is good and bad. We don't question the validity of these beliefs (e.g. truth is preferable over falsehood).
Ethics is an effort to reason our way through a dilemma, a deliberation to justify doing or not doing something when our values and belief system clash
The study of ethics should result in at least morally defensible decisions even if those decisions prove to be unpopular, and there are not always right or wrong answers, but there should always be "well-reasoned" ones