Where low-priority tasks figuratively reside. Typically used in the phrase "put (something) on the back burner." The phrase refers to the back burner of a stove, which is where pots are usually placed to simmer on low heat. I know you're eager to start on this new project, but I'm afraid it's going on the back burner—we just don't have the budget for it right now. You need to go to a doctor! You can't put your health on the back burner any longer!