A receiver was an electronic device which received and converted a signal into sound or vision.
In the 32nd century, in the case of Grudge becoming lost, Cleveland Booker installed a tracker in her collar. Using his receiver, Booker could locate his cat by homing in on the tracker's signal. In 3189, Michael Burnham reverse-engineered the collar to find Booker on Hunhau. (DIS: "Scavengers")
In 3188, when examining a console on Booker's ship, Burnham recognized a receiver, along with other communications technology. (DIS: "That Hope Is You, Part 1")