Handle is a new concept which was introduced in Lens v2.

Think about Handle as a name on a social network: like @alice, @bob or @vitalik.

Handles can exist and can be minted separately from profiles, and then can be linked and unlinked from one profile to another.

Handles exist in their own namespaces, and currently the only namespace is lens, so all currently available handles are technically under lens/alice.

The Handle part that follows the namespace is usually referred to as "local-name".