The McKinney-Vento Homeless Assistance Act (per Title IX, Part A of the Elementary and Secondary Education Act, as amended by the Every Student Succeeds Act) defines 'homeless'as follows:

The term "homeless children and youths" means individuals who lack a fixed, regular, and adequate nighttime residence, including

• children and youths who are sharing the housing of other persons due to loss of housing, economic hardship, or a similar reason; are living in motels, hotels, trailer parks, or camping grounds due to the lack of alternative adequate accommodations; are living in emergency or transitional shelters, or are abandoned in hospitals;

• children and youths who have a primary nighttime residence that is a public or private place not designed for or ordinarily used as regular sleeping accommodation for human beings;

• children and youths who are living in cars, parks, public spaces, abandoned buildings, substandard housing, bus or train stations, or similar settings; and

• migratory children (as such term is defined in section 1309 of the Elementary and Secondary Education Act of 1965) who qualify as homeless for the purposes of this subtitle because the children are living in circumstances described in clauses (i) through (iii).

The above definition has been adapted from the National Center for Homeless Education, and the full text of the McKinney-Vento Homeless Assistance Act can be read here.