@artyom
Raster tiles: A map image is ‘cut up’ into little squares: one set of image tiles per combination of style, language etc. This is replicated at all the required scales.

Vector tiles: The map data that would be required to display all the styles for that square is extracted from the database, simplified and stuck in an intermediate format. One set of tiles can support multiple styles, languages and angles that would be impractical with rasters.

@openstreetmap