placemat is a small mat or pad placed at an individual table-setting (as opposed to a full tablecloth, which covers the entire table). Their basic function is to mark a “place” at the dining table for a person, and to serve both protective and decorative roles.
A mosaic placemat gets its name from its design — instead of being plain, it features a pattern inspired by mosaic-art (that is, geometric / tile-like or tile-inspired patterns). These patterns can echo the look of traditional mosaics (many-coloured tiles, repeated symmetrical shapes, etc.) even if the placemat itself is not made of actual tile.