Good is a concept that is central to ethics and morality. It is also a topic of intense study within philosophy, religion, and other fields. The specific meaning and etymology of the word vary widely across languages and cultures, but all versions share an element of positive value. The term can be used as an adjective, a noun, or an adverb. It is commonly compared with its opposite, evil.

The concept of good has been a subject of extensive discussion since antiquity. One of the primary goals of most discussions has been to define what is good, in contrast with its opposite, evil. The biblical story of Adam and Eve’s eating from the “tree of the knowledge of good and evil” has influenced many discussions of goodness.

A common definition of good is that it is desirable, virtuous, or righteous. This definition reflects the importance of morality in most religions and philosophical traditions. Another meaning of good is that it is satisfactory in quality, quantity, or degree: a good job; a good house; a good education; healthy food; and so on. These two meanings of good are often linked to the broader idea of utility: what is good for people or things? Utility theories vary in their approach to this question. Some, such as hedonistic utilitarianism, advocate that the ultimate good for any individual is to maximize their pleasure. Others, such as desire-satisfaction utilitarianism, argue that the good for individuals is more complex and may include a combination of pleasure and other factors.

In modern usage, the word good is sometimes used as a synonym for well. However, good has a stronger connotation of positive value and intensity than well does. It is therefore appropriate to use it when expressing approval or satisfaction: The meal was good; I thought the speech was very good.

It is also possible to use the word good as an adverb: We waited a good while for Tom to arrive. The word good is often used in conjunction with other adverbs: Very good; fairly good; very well.

A defining feature of good is that it is different from and better than what came before it, or what could be expected to come before it. This is a key characteristic of evaluative terms, such as good and bad, that distinguish them from other types of words: it is easy for people to agree about the concept of good but still disagree about which concrete things are actually good (or bad). This distinction makes the term good particularly suitable for describing a subjective quality.