Semi-attached inside backs feature distinct cushions that appear to be loose but are in fact attached to the furniture by a section of fabric or leather. They offer the appearance of a loose pillow back but maintain more structure to keep the back cushions in place.
Loose pillow backs feature separate cushions that can be removed, flipped around, or shuffled. This type of back is common to more casual, relaxed designs and tends to be used on larger furniture.
Pullover (also called tight) inside backs do not have cushions at all, but instead have a single large panel with padding. They create a firmer, less "slouchy" seat, and also tend to be a little less deep than backs with full cushions. Many people prefer this design because back cushions, which are usually filled with either a fiber or a very soft foam, will eventually lose their "loft" and begin to appear less full than when the furniture was new; pullover backs do not do this.
Bustle backs feature two separate cushions: a lumbar cushion, and a shoulder/headrest cushion. Each is attached to the back only by its top edge. This back style is very popular for high-backed chairs as well as recliners and tilt-backs, as the design not only creates some visual interest but also provides excellent support.