Symbiosis is an ultra fancy term that means "the interaction between two species." And yes, it's ridiculously general. It could mean almost anything.
Symbiosis is just the umbrella term for cross-species interactions. There are 3 basic types, based on how the two species benefit from this "interaction."
Description: Both species benefit.
Mutualism is the awesome hippie share-the-love kind of symbiosis. Everyone gets in a circle, holding hands, and sings about... whatever it is hippies sing about. The classic example of this kind of symbiosis is the clown fish and the sea anemone.
The clown fish benefits by having a place to call home, and the sea anemone benefits from having a guard fish to protect it from intruders.
Description: One species benefits, and the other isn't harmed or helped.
Commensalism is not as lovey-dovey as mutualism, but no one is getting hurt, so it's still good. Commensalism is like giving a ride to someone who is on your way to your destination. The person you pick up definitely benefits because he doesn't have to spend money on gas or even find his car keys. You, as the driver, aren't inconvenienced because you were going that way anyway, but you don't get a big benefit from this interaction. (Unless the person slips you a fiver for gas, which is nice.)
Other examples include a bird building its nest in a hospitable tree,
or a hermit crab using a dead snail's shell. The snail will be dead, so what does he care?
Description: One species benefits. The other is harmed.
This is symbiosis for meanies. Unfortunately, there is no shortage of examples. There are all kinds of insects that make a meal of us and slip us some itchy poison at the same time. Diseases from viruses, bacteria, or protists fit in this category. And let's not forget fungal infections!
But let's stick to just one example, lest I give myself the jibblies thinking about all the bizarre parasites there are out there. Ep, too late. My skin is already crawling.
It's time for BED BUGS!
WARNING: If you are prone to the jibblies, you might not want to watch this, especially before bed time.