Leased lines are circuits or a combination of circuits designated to be at the exclusive permanent disposal of a given subscriber (or customer). A leased line connection is typically a dedicated point-to-point internet link for commercial use.
The Wikipedia leased line definition is "a private telecommunications circuit between two or more locations provided according to a commercial contract. It is sometimes also known as a private circuit, and as a data line in the UK. Typically, leased lines are used by businesses to connect geographically distant offices."