Externalities: Externalities are costs or benefits that affect parties who are not directly involved in a transaction. For example, pollution from a factory affects the health of nearby residents.
Public Goods: Public goods are non-excludable and non-rivalrous goods that are provided by the government because they would be underproduced or not produced at all by the private sector. Examples include national defense and street lighting.
Imperfect Competition: Imperfect competition refers to markets where there are few sellers or buyers, giving them some degree of control over price. Examples include monopolies and oligopolies.