Public goods are characterized by non-excludability and non-rivalry. Because private firms cannot easily exclude non-payers from consuming these goods, they lack the profit incentive to produce them, leading to market failure where these goods are under-produced or not provided at all by the private sector.

A free rider is an individual who consumes a good or service without paying for it. This phenomenon is prevalent with public goods because they are non-excludable; once the good is provided, it is impossible to prevent anyone from using it, regardless of whether they contributed to the cost of its production.

Common resources are goods that are rival in consumption but non-excludable. This means that while one person's use of the resource reduces the amount available for others (rivalry), it is difficult or impossible to prevent people from using the resource (non-excludability). This combination often leads to the 'tragedy of the commons' where the resource is overused.

Private goods are defined by two key properties: they are excludable, meaning owners can prevent others from using them, and they are rival in consumption, meaning one person's use of the good reduces the quantity available for others. Because of these properties, private goods can be efficiently allocated through market mechanisms where prices reflect the scarcity and value of the good.

Merit goods are goods or services that the government believes are beneficial for individuals and society, such as education and healthcare. In a free market, these goods are often under-provided because individuals may not fully appreciate their long-term benefits, or because they are unable to afford them. Consequently, governments often intervene by subsidizing or directly providing these goods to ensure they are consumed at a socially desirable level.

Excludability is a fundamental property of goods where it is technically and economically feasible to prevent non-payers from consuming the good. If a producer can easily restrict access to those who have not paid, the good is considered excludable. This is a key distinction in classifying goods alongside rivalry in consumption.

Common resources are goods that are rival in consumption but non-excludable. A national park is often considered a common resource because, while it is open to the public (non-excludable), the enjoyment of the space by one person can diminish the experience of others due to crowding (rivalry). Thus, it fits the definition of a common property resource.

The free-rider problem is the central obstacle for private provision of public goods. Because public goods are non-excludable, individuals have an incentive to wait for others to pay for the good while they consume it for free. This lack of incentive to contribute leads to market failure, where the good is either not provided at all or provided in insufficient quantities.

Non-rivalry in consumption means that the consumption of a good by one individual does not diminish the quantity or quality available for others. This is a defining characteristic of public goods, distinguishing them from private goods, which are rivalrous and whose consumption by one person prevents consumption by another.

A public good is defined by two key features: non-excludability and non-rivalry. Non-excludability means it is impossible to prevent people from using the good, and non-rivalry means that one person's consumption of the good does not reduce the amount available for others. These features make it difficult for private markets to charge for the good, necessitating government provision.