Something severed is cut off from its whole. A severed rope turns into two detached and individual pieces. In a severed relationship, people lose communication with one another.
To be severed is to be separated completely. Think of a tree branch being cut away from its trunk, or a connection being broken between two friends. The word comes from the Latin separare, meaning "to separate or pull apart." The adjective can refer to physical objects, like ropes or limbs, or to relationships and ties, such as friendships or contracts.