It sounds like a simple enough question – and there actually IS an answer. The Arizona State Legislature (azleg.gov) site provides the answer:
A homeowners’ association (HOA) is a common interest organization to which all the owners of lots in a planned community or owners of units in a condominium must belong. The four defining characteristics of all HOAs are:
• all owners are automatically members.
• governing documents create mutual obligations.
• mandatory fees or assessments are generally levied against owners and used for the operation of the association
• owners share a property interest in the community.
To read the entire BRIEF, click here