Polyurethane

Polyurethane is a synthetic resin film finish, technically a type of varnish formulated with polyurethane resins for extra hardness and abrasion resistance, and by a wide margin the most common film finish reached for on modern furniture, floors, and tabletops. Oil-based polyurethane ambers slightly and deepens wood tone over time, similar to traditional varnish; water-based polyurethane dries faster, stays clear rather than ambering, and has much lower odor, at a modest cost in outright toughness compared to the oil-based version.

Like other film finishes, it trades an oil finish's easy, low-drama touch-up process for genuinely stronger protection against water, heat, and scratches -- the right call for a surface that's actually going to take daily abuse, less necessary for furniture handled gently.