Will add on that of course both terms ultimately refer to the same thing, but each has a slightly different focus on the exact roles of the kink. The term "feederism" like Clair said is by far the most widely used, and it is also the oldest, but many in the community tend to reject it as it implies that there is a central role, being that of the feeder, and further carries the implication that feedees are simply the passive objects of focus in the kink for feeders rather than active, willing participants in their own right. So chopping off the -er and calling it just "feedism" is more inclusive since it instead puts focus on the action of the feed itself rather than any one person and also leaves more room for other roles like admirers and encouragers. I also personally prefer feedism as a term since it feels to me more like a community than just subject to the whims of just one particular role in the kink, but more people will be able to find this site if it's feederism.org for the reasons I said earlier.
