Mosaics are
a.
images made with glass that has been colored by metallic salts are pieced together like a collage, and are joined by leading.
b.
images made by arranging colored pieces on a flat surface, which are held using leading.
c.
artwork created by arranging cut out or torn material pasted onto a surface. means "to glue" in french.
d.
images made by arranging stones or tiles that are then embedded with a filler to connect the colored pieces.