Chair: A piece of furniture
for one person to sit on,
with a back, a seat and four legs.
(Oxford Learners Dictionary)

Is a tree stump a chair?
Yes, if you can sit on it.
(Jordan B Peterson, Maps of Meaning)

57 Chairs is a tribute to an often overlooked category of objects: The street chair. Being shared by many – marketers, parking attendants, or bypassers needing a rest – street chairs are collective goods, free of ownership. If chairs are defined by their meaning to human beings, by their potential to interact with us, then the street chair is the queen of all chairs. Used, reused, moved around, sat on, barely repaired and supplemented thousands of times, they are monuments of endless, manifold human-chair-interactions.