The larger of the two members of a symbiosis is usually called the 'host', and the smaller is a 'symbiont'. The term is often understood as referring to obligatory, mutually beneficial relationships, but such 'mutualism' is but one category of symbiosis. Other categories include 'parasitism', 'commensalism', 'amensalism' and 'neutralism'. Alternatively, one can distinguish 'ectosymbiosis' from 'endosymbiosis'.