Culture is a word that everyone is familiar with, but its precise meaning can be elusive. A useful definition by noted social scientist Geert Hofstede is that culture consists of shared mental programs that condition individuals' responses to their environment. There are three levels involved in the mental programing: The deepest level--human nature--is based on common biological reactions, such as sex, drive, hunger and territoriality that all members of the human race have in common, even though they come from different cultures. The middle level--culture--is based on common experiences that we share with a particular group of our fellows. Cultural values, attitudes and assumptions about proper behavior give us something in common with a definable group of others, but not with all of them. The group may be a very large one, such as a national population, i.e. Japanese culture; or a very small one, i.e. the culture of the committee of a local parent-teacher association. The shallowest level--personality--is based on the specific genetic makeup and personal experiences that make each of us a unique individual. For example, we may be sociable or introverted, aggressive or submissive, and emotional or stable. We all have many behaviors and understandings that are quite different from those of others, even though we come from the same culture. Culture also has the following basic characteristics. First, culture is mental programming that a group has in common that is not normally available to people outside the group. Second, the mental programing of a group is learned by its members over long periods as they interact with the environment and with each other. Third, the mental programming involved is strong. People have a hard time escaping their culture even when they want to. Fourth, culture is not random as it is a system of values, attitudes, beliefs, and meanings that are related to each other and to the context. Last, much of culture is concealed. Besides immediate surface behaviors, such as body language, and physical artifacts like art, culture also involves the underlying values, social structures, and ways of thinking.