Kneeling position, with outstretched or raised toes; the term is also used for sitting down.
An upright but relaxed posture is typical for seiza - it speaks of the kneeling person's attentive mind.
During meditation or while watching the teacher's presentation, the toes are usually flat on the ground. When engaged in suwari-waza techniques or ukemi, the person in seiza is usually raised on their toes.
Seiza as a sitting-down movement is praticed to improve balance, posture and focus.
Search "Basic Forms" page for videos showing SEIZA