A market town is a European settlement that obtained by custom or royal charter, in the Middle Ages, a market right, which allowed it to host a regular market; this distinguished it from a village or city. In Britain, small rural towns with a hinterland of villages are still commonly called market towns, as sometimes reflected in their names (e.g. Downham Market, Market Rasen, or Market Drayton).
Modern markets are often in special halls, but this is a recent development, and the rise of permanent retail establishments has reduced the need for periodic markets. Historically the markets were open-air, held in what is usually called (regardless of its actual shape) the market square (or "Market Place" etc), and centred on a market cross (mercat cross in Scotland). They were and are typically open one or two days a week.