A Shop is any place where players can buy and/or sell items of different kinds to and from a non-player character. Shops have a higher price compared to purchasing items from other players, and once you have to sell an item, it is much lower than a player's sell price. However, some shops disregard this fact, as this is simply a pattern found by players.
Shops have various types and located in various locations. Inside shops are always non-player characters which players can right-click and select trade, however, a few can simply be left-clicked. Here are shops that can be located in RuneScape.