Pieces with no arms may include certain armless sectional components, ottomans, and some styles specifically designed to be armless.
Sock arms completely envelop the entire arm in a single upholstered design. This is achieved either by sewn components in the arm upholstery, or by carefully upholstering the fabric or leather in a "sunburst" multi-folded design. These tend to be a more casual style.
Panel arms feature a flat piece (usually upholstered, though sometimes done in wood) which is attached to the front of the arm and often highlighted by a border in welt cord or nailhead. Panel arms usually create a more traditional style.
Track arms are less padded than sock or panel arms, and do not wrap around to extend beyond the outside edges of the furniture. They make a sleek, contemporary look.
Pullover arms are a mix of sock and track arm styles, featuring the padded comfort of the sock arm but in the narrower design of the track arm. They are well suited to either casual or contemporary designs.
English arms (also called Charles-of-London arms) feature curves and elegant styling, and often go with a scroll back design. They are ideal for more formal settings.
Wood arms often feature a small amount of upholstered padding, but are more intended for formal settings.