Which of the following best defines a public good?

A public good is best defined as a commodity or service that is provided to all members of a society without exclusion. This means that once the good is produced, it is available for use by everyone, regardless of whether they pay for it or not. Public goods are characterized by two main properties: they are non-excludable, meaning individuals cannot be effectively excluded from using them, and they are non-rivalrous, meaning one person's use of the good does not diminish its availability for others.

In contrast, the other options mention conditions or characteristics that do not align with the definition of public goods. A service provided solely to individuals who pay for it describes a private good, while programs funded by private donations do not automatically qualify as public goods, as they may not be accessible to all. Similarly, a good that only benefits the wealthy conflicts with the inclusive nature of public goods, which are intended to serve the entire community regardless of socio-economic status.