The McKinney-Vento Definition of Homeless
Subtitle VII-B of 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"--
(A) means individuals who lack a fixed, regular, and adequate nighttime residence (within the meaning of section 103(a)(1)); and (B) includes--
(i) 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;*
(ii) children and youths who have a primary nighttime residence that is a public or private place not designed for or ordinarily used as a regular sleeping accommodation for human beings (within the meaning of section 103(a)(2)(C));
(iii) children and youths who are living in cars, parks, public spaces, abandoned buildings, substandard housing, bus or train stations, or similar settings; and
(iv) 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).
*Per Title IX, Part A of the Every Student Succeeds Act, "awaiting foster care placement" was removed from the definition of homeless on December 10, 2016; the only exception to his removal is that "covered states" have until December 10, 2017 to remove "awaiting foster care placement" from their definition of homeless.