Although you will often see people writing about the “backseat” of a car, the standard and still most common spelling of the noun form is as two words: “back seat.” “Small children should ride in the back seat.” “In a crisis, planning takes a back seat to immediate action.”

The one-word adjective “backseat” is appropriate when it describes where something is. “The backseat area is cramped in this model ” “Don’t be a backseat driver.” Conservatives prefer the hyphenated spelling “back-seat” for this sort of use: the back-seat area, a back-seat driver.