A small hamburger; or anything that slides or a control device that moves back and forth to adjust something.
From 'slide' (Old English 'slīdan') plus '-er' suffix. The hamburger meaning emerged in 1900s-1920s slang, possibly because burgers 'slide' down easily or were served on slider rails.
White Castle, America's oldest hamburger chain (founded 1921), made the slider famous by calling their small burgers 'sliders'—the name caught on because it's irresistibly cute and perfectly describes how easy they are to eat quickly.
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