Symbiosis

I'm pretty sure that this is what I learnt in 'O' Level Biology. It appears however that either my memory has let me down, or I learnt wrong, or the definition has changed (and one of these possibilities must also apply to the setter of this question).

Symbiosis is now defined (by North Carolina State University, for example, and also by our old friend Wikipedia) as "any interaction where two species live together in close physical association". If one species benefits and the other is harmed, the relationship is parasitic; if one species benefits, and the other doesn't benefit but is not harmed either, it's commensal; if both species benefit, it's mutualistic.

Parasitism I remember; but I don't remember being taught about commensalism or mutualism.

There is a fourth possibility as to why what I think I learnt in 'O' Level Biology (and what the setter of this question believes) appears to be wrong. It's that we learnt the British version, and the versions given by NCSU and Wikipedia are American.