Friendship may entail putting on a crazy hat for a photograph.

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Friendship is a type of relationship between two people who care about each other. But such a dry definition doesn't do the concept of friendship justice. Consider these examples: A friend is the first person you want to call when you hear good news. A friend remembers that you don't like pickles on your sandwich. A friend will accompany you on the most boring of errands and make them seem fun.

In other words, friendship is wonderful, and much ink has been spilled in citing the virtues of having friends. That's not to say friendship is easy, though. It demands time and effort, and it requires that people put someone other than themselves first sometimes. But in exchange for that work, a friend can provide an immense amount of support and comfort in good times and in bad.

Many qualities are necessary for a good friendship, including honesty, trustworthiness, loyalty and unconditional acceptance. A friendship should make both people in the relationship happy; both people should have fun when they spend time together. To be perfectly frank, that's a tall order. Human beings can clash very easily, which is why it's hard for some people to maintain many friendships. It's possible that friendship can exist between two people at one stage of life, but life changes and personal growth may make friendship impossible at another stage. It can be hard to meet the people who would make the perfect friend. A 2006 study found that people living in the United States had fewer friends than ever, with 1 in 4 Americans claiming they had no one to confide in [source: Kornblum].

Pop culture often reflects what our society thinks about friends. In recent years, the concept of bromance, or a close friendship between two men, has taken center stage in films such as "I Love You, Man," and television series such as "Scrubs." Male friendships, if these examples are any indication, include everything from playing video games to listening to music to talking about girls. "Sex and the City" is often cited for its influence on female friendships. The long-running television show and subsequent movies depict female friends shopping, drinking and gossiping together. Opposite-sex friendship, or friendship between a male and a female, is a bit trickier for our society; thanks largely to the film "When Harry Met Sally," people tend to think that sex will elevate a friendship to a romance. For that reason, opposite-sex friendship is usually depicted on-screen between a heterosexual woman and a gay man, such as on the show "Will & Grace." Because sex is off the table, people will buy in to the idea that these two people can be there for one another as friends.