A Teisho is a talk by a sanctioned teacher, usually given during an intensive meditation retreat known by the Japanese term sesshin. The teacher sits on a raised platform and faces the Buddha altar, not the meditators. The teacher thus directs the Teisho to the Buddha, and this helps the teacher raise the Teisho to the highest level.
A Teisho differs from a Dharma Talk which is a talk by a senior student who has not received sanction to teach. The speaker faces the sangha during the talk and sits on his or her normal cushions, there being no raised platform in use. Dharma talks are typically given during regular meetings of the meditation group and usually supplant a round of meditation. Master Hakuin’s chant is not recited prior to a Dharma talk.
Although Zen practitioners sit without motion during periods of formal zazen, most Zen centers have a rule that allows the listeners to adjust their posture during a Teisho or a Dharma talk because listening is the paramount activity during either talk.