Plural of backseat; the rear seating areas in a vehicle or venue, or to take a backseat means to become less important or to yield responsibility.
Compound of 'back' and 'seat' (Old English 'sittan'). The figurative sense developed from the literal position of being behind the driver.
The phrase 'take a backseat' is fascinating because it uses spatial language (back = less important) that appears in almost every human language—our brains literally map importance onto physical position, which is why 'front and center' means priority.
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