It can be thought of as a form of "biological barter" since the species trade resources (for example carbohydrates or inorganic compounds), or services such as gamete or offspring dispersal, or protection from predators.
Word origin: L. mūtu(us): mutual, reciprocal + Gk -ismos, -isma: often directly, often through.
Related forms: mutualist (noun), mutualistic (adjective).
Compare: amensalism, commensalism, parasitism.
See also: cooperation, symbiosis.