What is Assured Tenancy?

Legal Definition
An assured tenancy is a legal category of residential tenancy to an individual (or individuals jointly) in English land law. Statute affords a tenant under an assured tenancy a degree of security of tenure. A tenant under an assured tenancy may not be evicted without a reasonable ground in the Housing Act 1988 and, where periodic, changes in rent are potentially subject to a challenge before a rent assessment committee.

Assured tenancies were introduced by the Housing Act 1988 that applies to tenancies entered from its commencement date or those assured tenancies it converted from the Housing Act 1980. The Act replaced most of the greater rent protection under the Rent Act 1977 and in rarer cases, other Rent Acts. However, since 28 February 1997, all new residential tenancies with three exceptions are deemed to be assured shorthold tenancies. These exceptions are those excluded by notice before or after the tenancy, those specifying it is not a shorthold, and lettings to existing assured tenants.
-- Wikipedia
Legal Definition
When a tenant pays an open rent rate. The rules are a landlord cannot reposess property unless certain rules are broken, rent is raised at market level with a cap, and a tenant can't give a third party tenancy without a landlords signature. AKA protected