For telephone installations.  This RJ11 jack includes 4 screw terminals on the inside to connect the wires to.  No punch down tools are required.  Supports two lines (2 wires for line 1 and two wires for line 2.) 

Looking at the actual jack, the inside 2 wires are the first line and the outside 2 wires are the second line, which is industry standard wiring.