What is the official definition of homelessness?

An individual may be considered to be homeless if that person is “doubled up,” a term that refers to a situation where individuals are unable to maintain their housing situation and are forced to stay with a series of friends and/or extended family members. In addition, previously homeless individuals who are to be released from a prison or a hospital may be considered homeless if they do not have a stable housing situation to which they can return. A recognition of the instability of an individual’s living arrangements is critical to the definition of homelessness. (HRSA/Bureau of Primary Health Care, Program Assistance Letter 99-12, Health Care for the Homeless Principles of Practice)

Source: https://www.nhchc.org/faq/official-definition-homelessness/