The last time we spoke to the South Hams council press office, they didn’t know what affordable housing was. For them, and for us, here’s a definition from the Communities and Local Government site

Social and affordable housing
Affordable housing includes social rented and intermediate housing, provided to specified eligible households whose needs are not met by the market. Affordable housing should:
• meet the needs of eligible households including availability at a cost low enough for them to afford, determined with regard to local incomes and local house prices; and
• include provisions for:
1. the home to be retained for future eligible households; or if these restrictions are lifted, for any subsidy to be recycled for alternative affordable housing provision.
2. Social rented housing is rented housing owned and managed by local authorities and RSLs, for which guideline target rents are determined through the national rent regime. It may also include rented housing owned or managed by other persons and provided under equivalent rental arrangements to the above, as agreed with the local authority or with the Homes and Communities Agency as a condition of grant.
Intermediate affordable housing is housing at prices and rents above those of social rent but below market price or rents, and which meet the criteria set out above. These can include shared equity (eg HomeBuy) and other low cost homes for sales, and intermediate rent.