A dumpy, medium-sized wader with a medium-short bill and legs, and a distinctive grey rump. It is very quiet for a wader, lacking loud alarm calls. It is typically very gregarious and individuals can be extraordinarily tame.

Knots are especially sociable, feeding in dense flocks on open mud flats. They advance like a grey carpet: even there are only a hundred or so they jostle almost shoulder-to-shoulder. When disturbed, or moving to their roosts as the tide rises, airborne flocks are wonderfully impressive as they twist and turn like columns of smoke in turbulent air.