Scale describes the ratio in size between something in the real world and its representation on a map. In other words, if a map has a scale of 1:50 000 then a distance of 1 cm on the map represents 50 000cm (500 m) in the real world.
The main scales used by Ordnance Survey (OS) for surveying are 1:1250, 1:2500 and 1:10 000. These are referred to as large scale maps, which is when features in the real world are portrayed larger on the map.