For tobytub and glass-addiction - opus (laying techniques)
I am paraphrasing from my favorite mosaic book Classic Mosaic by Elaine M. Goodwin. The way tesserae are laid out are called the Opus. Opus Tessellatum is where the image is surrounded by one or two bands of tesserae to define its form. Opus Vermiculatum is when the tesserae resemble vermicelli, or curved lines. Opus Musivum occurs on larger floors (overall design). Opus Palladianum - random shapes. Andamento, the way in which the tesserae are made to flow in directional lines ...rhythm, movement.