If you ask someone what "friendship" is, you'll likely hear that it's a relationship between people who care deeply for each other. Ask what qualifies as being a "good friend" and you might hear the words "honest," "loyal" and "trustworthy" along with "excellent listener." And you might learn that friends should have fun together and make each other happy but must also be on hand to help each other through bad times, accepting quirks and faults without judgment. But if you ask someone else, perhaps on a different continent, you could get a different response. According to an article in Science Daily, for example, friendships in the U.S. and Japan can differ greatly -- especially in regard to what friends are willing to share with each other.

Apparently, in the U.S., it's common for friends to disclose pretty personal information -- including intimate details of their other relationships and any problems they might be facing -- but in Japan, such disclosures aren't as commonplace [source: Science Daily].

How you select your friends can depend on your age. Although one study in the Journal of Neuroscience indicated that social closeness is more relevant than common interests and similarities, another study (of teenaged subjects) suggests that matching personality traits are key [sources: Bloomberg Businessweek and ]. Reportedly, the study indicated "that the image young people have of their friends is more important than the actual character of these friends" and that "they look for similarities in personality."

No matter how you identify your friends, though, many scientists and physicians agree that having them can be beneficial to your emotional and physical health -- even keeping germs at bay [source: Rudin]. Friendship is closely tied to happiness -- some suggest it has a more profound effect on happiness levels than income. In fact, the BBC reported, "One economist, Professor Oswald at Warwick University, has a formula to work out how much extra cash we would need to make up for not having friends. The answer is £50,000" [source: Rudin].

And it looks like finding friends isn't only a human need: Certain animals -- bats, dolphins, elephants and primates -- make friends, too [source: Viegas].