Armbinder is a loose term designating a range of restraint devices primarily used in bondage play (rather than law enforcement, medicine, or psychiatry), their common function being to bind the arms and/or hands to each other or to the body, usually behind the back. The most common form is the monoglove, and in some usage the term functions as if a direct synonym for 'monoglove'; but a wide range of other forms exists (see external link).
It consists of a sheath, roughly conical, that encloses both of the wearer's arms, holding them together behind the back, combined with one of various harness arrangements to hold it in place. The sheath itself typically covers the arms from the fingertips to above the elbows, and is closed and tightened with a zipper, lacing, or both; the sheath is frequently supplemented with straps around the wrists and the elbows or upper arms. The sheath alone is ineffective without a harness to keep it from slipping down the arms; the most common harness is a pair of straps that join to the outer top of the sheath, run over the shoulders and under the armpits, and join again at the inner top of the sheath. The straps are usually crossed, behind the neck or across the upper chest, to prevent the straps from slipping off the shoulders. The latter position can cause problems if the straps tend to ride up and press on the wearer's throat.