Gassho is Japanese for "palms of the hands placed together." The gesture is made as a greeting, in gratitude, or to make a request.
In the most common form of gassho used in Japanese Zen, hands are pressed together, palm to palm in front of one's face. Fingers are straight. There should be about a fist's distance between one's nose and one's hands. Fingertips should be the same distance from the floor as one's nose. Elbows are held slightly away from the body.
Holding the hands in front of the face signifies nonduality. It signifies that the giver and receiver of the bow are not two.
Gassho often accompanies a bow. To bow, bend only at the waist, keeping the back straight.