Is this a plug or the heating cable?

It is a plug that controlls what you plug into it.

This device is a temperature-controlled switch that accepts a grounded male connector which is usually a length of pipe heat tape. The device itself gets plugged in to an electrical outlet or extension cord. If your pipe heat tape has no thermostat of its own, this device is the only way to manage when the tape is powered on or off.

this is a cold sensing plug in adapter that turns on when it is below 38 degrees.