Symbiosis: A close ecological relationship between two or more organisms of different species that live in direct contact with one another. Like having roommates – you share space and resources!
Commensalism: A type of relationship where one organism benefits but the other isn't affected either positively or negatively. Imagine if your friend got free concert tickets because you're performing - they benefit but it doesn't affect you either way!
Parasitism: A non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other. It's like a friend who always takes but never gives back.