What are insulation displaced connectors

Insulation displacement connectors are connectors which can be mounted directly over an insulated wire without stripping the insulation.  These connectors come with a sharp blade like arrangement which slices through the insulation and makes contact with the conductor.  

The blade and the conductor are cold welded to form a strong connection.  Insulation displacement connectors are used in telephone and network circuits.  Ribbon cables are generally used with insulation displacement connectors.  Ethernet cables are also mounted to insulation displacement connectors.