Etiquette is a set of practices and forms which are followed in a wide variety of situations; many people consider it to be a branch of decorum, or general social behaviour. Each society has its own distinct etiquette, and various cultures within a society also have their own rules and social norms. Learning these codes of behaviour can be very challenging for people who are new to a particular culture, and even old hands sometimes have a rough time.
The rules of etiquette govern how people behave. For example, the concept of greeting people politely and with respect is common to the codes of behaviour of many cultures, although the way in which that respect is expressed may vary. In some Asian countries, for example, people may bow or clasp their hands together when greeting someone, while in the United States, people often shake hands, or hug each other in some subcultures.
It is safe to assume that there is an etiquette role for pretty much every situation one might encounter, from meeting the President of the United States to politely declining a meal in the Middle East. Because the social norms of different cultures are so different, many people study etiquette before traveling or entering a new social circle to ensure that they do not cause offense or embarrass themselves.