Young Blonde Girl With The Old Chair And The Mirror

A chair may or may not have armrests; chairs with armrests are termed armchairs. In French, a distinction is made between fauteuil and chaise, the terms for chairs with and without armrests, respectively. If present, armrests will support part of the body weight through the arms if the arms are resting on the armrests. Armrests further have the function of making entry and exit from the chair easier (but from the side it becomes more difficult). Armrests should support the forearm and not the sensitive elbow area. Hence in some chair designs, the armrest is not continuous to the chair back, but is missing in the elbow area.
A couch, bench, or other arrangement of seats next to each other may have armrest at the sides and/or arm rests in between. The latter may be provided for comfort, but also for privacy e.g. in public transport and other public places, and to prevent lying on the bench. Arm rests reduce both desired and undesired proximity. A loveseat in particular, has no armrest in between.
There are also seats in movie theaters, and pictures of benches with and without arm rests.