When two different organisms live together in a close relationship where at least one of them benefits, that's symbiosis. The word comes from Greek roots meaning “living together.”

Symbiotic relationships take different forms. Sometimes both creatures benefit: clownfish shelter safely among sea anemone tentacles while keeping the anemone clean and bringing it food scraps. Flowers provide nectar to bees, and bees spread the flowers' pollen to help them reproduce. These partnerships work because each organism gives something the other needs.

Other times, only one partner benefits while the other isn't helped or harmed. Remora fish attach to sharks and eat leftover food, while the shark barely notices they're there. Birds build nests in trees, taking advantage of the height and shelter without affecting the tree much at all.

A symbiotic relationship can even be harmful to one partner, like when a tick drinks blood from a dog. The tick benefits, but the dog suffers. Scientists call this parasitism, and while it's not the friendliest type of symbiosis, it's still two organisms living in very close connection.

The term has spread beyond biology. People describe symbiotic friendships or business relationships where each person or company provides something valuable to the other. A comic book writer and artist might have a symbiotic partnership, each making the other's work better.