A public good is a type of product or service that is available for everyone to use, and one person's use does not reduce its availability to others. Examples include clean air, national defense, and public parks. These goods are typically provided by the government or community because they benefit society as a whole. Public goods are characterized by two main features: non-excludability and non-rivalry. Non-excludability means that it is difficult to prevent anyone from using the good, while non-rivalry indicates that one person's consumption does not diminish the ability of others to consume it. This makes public goods essential for promoting social welfare and equity.