이요

Polite 요 on a one-word reply

Sticks the polite 요 straight onto a noun so a fragment can stand as a complete, courteous turn. It is how you echo back what you just heard, usually in surprise — 'Seoul Science Center?', 'Shrink art?' — and also how you order ('Then I'll have the most expensive one!') or hand something over ('Your gum'). Because it is only a fragment, the situation has to supply the rest; the full sentence would use 이에요, 'it is'.

Register: polite but casual and fragmentary