In Japan, people greet each other by bowing. A bow ranges from a small nod of the head to a long, 90 degree bend at the waist. Bowing is considered extremely important in Japan, so much so that, although children normally begin learning how to bow from a very young age, companies commonly provide training to their employees in how to execute bows correctly.
A Westerner probably won't notice the sophisticated use of the bow in Japanese culture. The Japanese bow to one another as a greeting, a parting gesture, a way of expressing humility, respect or apology, and an alternative to waving or saying "Hi." The Japanese often bow every time they meet someone, even if they have already seen that person several times that day. Sometimes they even bow to each other while they are riding bicycles.
There are four bows, each with a different meaning:
The nod-bow, 5 Degrees: This is just a small nod of your head. The simplest, (which is reserved mostly for pretty good friends and therefore the least casual of all bows), is at an angle of five degrees. You can also use this bow if you are higher in rank (in terms of society, work etc.) than the person you're bowing to.
The other three more common types of ways to bow, are called eshaku, keirei, saikeirei.
The degree of the bow expresses the level of respect towards the other person. In general bowing by about 15% is regarded as sufficient – especially for foreigners. When bowing to someone of higher social status, a deeper, longer bow indicates respect. Conversely, a small head nod is casual and informal. However, most Japanese do not expect foreigners to know proper bowing rules and so a nod of the head is usually sufficient.
Greeting Bow, Eshaku (会釈), 15 Degrees: This bow is for greetings, mostly for people you already know or are equals with. The 5 degree bow” above is similar, but for when you know someone a lot better. This bow is probably for people you’ve met before and are familiar with, but not familiar enough to just go for the nod.
Respect Bow, Keirei (敬礼), 30 degrees: This is where bowing gets respectful. Thirty degrees is actually quite a lot and feels like quite a lot, if you go ahead and do it. This bow is reserved for your boss / other people who are higher ranking than you. You could probably do a little more than 30 degrees if you wanted to, too. You wouldn’t use this bow with good friends or relatives (unless you were making a joke), so save this for people you don’t know / people who are above you on that societal scale.
Highest Respect Bow, Saikeirei 最敬礼, 45 degrees: This bow conveys deep respect or an apology.
You only ever bow lower than 45 degrees if the other person is extremely higher status to you, which is why Obama caused such an uproar in the U.S. back in 2009 when he bowed at 90 degrees to the Japanese Emperor, as seen in the video below.
Critics claimed the sign of deference went against state department protocol, which decrees that presidents bow to no one. These deep bows are performed by people in inferior positions, for example you will see car salesmen bowing deeply to customers leaving their parking lot. You also see clerks giving deep bows to customers in department stores and students giving deep bows to their teachers. Yes, it is a sign of respect, but it is a sign of respect given by a person in an inferior position to someone else who is in a superior position. On the other hand, very low bows like this are a sign of great respect and deference to a superior in Japan, but as for this incident, I'm sure the Japanese people just brushed it off as a simple 'goof'.
As for the etiquette on bowing:
Bow with a straight back and eyes cast downward. The hands stay pinned to the side, feet together and you bow straight at the waist. A lot of Americans bring their hands together like they're praying but that's not the right way to do it.
There are differences between the way women and men bow. Whereas men keep their hands at the side of the body, women put the hands in front of the body.
Don't bow more for than a couple of seconds except when praying. Sometimes Japanese bow slightly to one side so they don't bump heads with the person they are bowing to.
To be polite bow as low or lower than the person you are bowing to. It is also a good idea to lower your eyes and keep you hands and fist unclenched against your side.
Welcome girls at Japanese department stores greet every customer with a bow. A columnist with a Tokyo newspaper once calculated that an average welcome girl bowed 665,600 times a year if she worked a five day work-day and 798,720 times if she worked six days.
While researching this question, I came across, several times, of an interesting mention of a recent five-year period of which twenty-four residents of Tokyo died while bowing to each other!
Source(s): japan-guide.com/, about.com/, afscottd.blogspot.com/, tofugu.com/, latimesblogs.latimes.com/, hoshuha.com/, factsanddetails.com/