Bowing is the act of lowering the head, or sometimes the entire upper body from the waist/hip, as a social gesture. Sometimes bending one's knee is also called bowing. Bowing is used as a gesture of greeting or respect, as a sign of reverence, subordination, or shame. The depth of the bow expresses degree of respect or gratitude.
To bow is also a metaphorical expression that means to submit or yield to another's wish or opinion.
Bowing is common around the world, but is especially prominent in East Asian cultures such as China, Korea, and Japan. In European cultures, bowing used to be an exclusively male practice - females would perform a related gesture called a curtsey.
In European courtly circles, males were expected to "bow and scrape" (hence the term "bowing and scraping" for what appears to be excessive ceremony). "Scraping" refers to the drawing back of the right leg as one bows, such that the right foot scrapes the floor or earth. Typically, while executing such a bow, the man's left hand is pressed horizontally across the abdomen while the right is held out from the body.
In Western cultures today, bowing is most common by actors or performers at the end of a concert or play in order to acknowledge the applause of the audience.
Bowing to other human beings is frowned upon in Muslim cultures as all human beings are considered equal and bowing is only supposed to be done to God in Islam.