/ˈmyo͞oCHo͞oəˌlizəm/
Noun
1. The way two organisms of different species exist in a relationship in which each individual benefits. Similar interactions within a species are known as co-operation. Mutualism is a type of symbiosis. (wikipedia.org)
2. Symbiotic interaction between different species that is mutually beneficial. (wikipedia.org)
3. Any interaction between two species that benefits both; typically involves the exchange of substances or services. (wiktionary.org)
4. The relation between two different species of organisms that are interdependent; each gains benefits from the other. (wordnetweb.princeton.edu)
Word origin: from Latin mutuus “reciprocal, done in exchange.”