Refers to a branch location of a store or business, as opposed to the main store.
このラーメン屋は都内に三つの出店がある。
This ramen shop has three branches in Tokyo.
A temporary or small shop set up at a festival, market, or on the street.
祭りでたこ焼きの出店を出した。
We set up a takoyaki stall at the festival.
出店 refers to a temporary booth set up for an event, whereas 屋台 usually implies a food-selling cart or stall specifically.
Compound of 出 (de, 'out') + 店 (mise, 'shop'). The reading でみせ is a straightforward combination of the kun'yomi readings of the two kanji.