(The following is extracted from the NPPF Annex. 2 Glossary)

Rural exception sites: Small sites used for affordable housing in perpetuity where
sites would not normally be used for housing. Rural exception sites seek to address
the needs of the local community by accommodating households who are either
current residents or have an existing family or employment connection. Small
numbers of market homes may be allowed at the local authority’s discretion, for
example where essential to enable the delivery of affordable units without grant
funding.