Culture and Social Structure
Culture is a difficult thing to strictly define. Such a large variety of societal aspects fall under its realm, that it's sometimes complicated to draw a line between what is part of a culture and what is not. To put it in extremely vague terms, culture is a way of life. All the traits that make up a particular society, from religious beliefs to modes of dress to art to methods of farming, build up a culture. Culture includes the good and the bad, the old and the new, the strong and the weak - essentially it includes "everything".
Many varieties of cultures exist. There are the obvious ethnic cultures - African-American culture, Latino culture, Greek culture, etc., each with their own foods, art, religion, familial roles, and values. American culture, for example, is generally considered to be relaxed - apple pie, blue jeans, baseball and the like.
Family roles are not set in stone, there is freedom to choose a religion based on one's own comfort (or choose no religion at all), and while a certain level of morality is maintained, values are generally loose.
Compare this to the culture of the remote parts of India. There, a woman is required to serve her husband and his family, even after his death. They are very devout, and there is only one religion to "choose" from. They are held to a strict moral code, and anyone who violates this code is considered an outcast.
There are many other ways to consider culture. There is the culture of a particular age group. A septuagenarian has a way of life very different than that of a teenager. His music, dress, beliefs, and goals are generally dissimilar to those of his younger counterpart.
Or there is the...