burn·er 
(bûrnər)
(bûrnər)n.
Idioms: 1. One that burns, especially:
a. A device, as in a furnace, stove, or gas lamp, that is lighted to produce a flame.
b. A device on a stovetop, such as a gas jet or electric element, that produces heat.
2.
a. A unit, such as a furnace, in which something is burned: an oil burner.
b. An incinerator.
c. See combustor.
3. A sharp pain caused by compression of a nerve, often resulting from a sports injury. Also called stinger.
4. An inexpensive cell phone, especially one for which usage is paid in advance and which can be thrown away easily if necessary: “Ana hasn't shown up to her waitressing job ... for three days, the address her boss has on file is a dead end, and her cell phone is a burner” (Jessica Derschowitz). Also called burner phone.
on the back burner
As a low priority: kept the project on the back burner all summer.
on the front burner
As a high priority.