A chair is a piece of furniture that seats one person. There were several period forms in heraldry. The default chair has a high, straight back; it’s sometimes explicitly blazoned a “backed chair”. It’s a period charge, found in the arms of von Döltzky, 1605 [Siebmacher 144]. This form of chair is drawn in trian aspect for better visibility.
There is also the “curule chair”, sometimes blazoned an “antique chair” or “chair of estate”, backless and ornate; it was the badge of the Earls of Oxford, c.1550, in their capacity as Lords Chamberlain [HB 132, Siddons II.2 302; cf. de Bara 157]. The curule chair is affronty by default.
Related to the chair is the “stool”, a low three-legged seat that’s more portable and less formal than a chair. It too is period, found in the arms of Schöner von Strubenhart, 1605 [Siebmacher 121].
Herjólfr Eilifsson bears: Argent, a wooden chair bendwise proper.
Raymond the Gruesome bears: Azure, in pale a sun-wheel bendwise conjoined to a curule chair Or.
Helen of Greyfells bears as a badge: A wooden three-legged stool proper.