Welfarism is the view that what's good (simpliciter) is just welfare, i.e. things being good for various individuals. (Note that this can aggregate: saving two lives is better than just saving one, but there's no larger entity that it is better *for*.)
By contrast, a nihilist might agree that something is "good for" an individual, but deny that this *matters* in any way. That is, they would deny that welfare is good (simpliciter).
Welfarism is the view that what's good (simpliciter) is just welfare, i.e. things being good for various individuals. (Note that this can aggregate: saving two lives is better than just saving one, but there's no larger entity that it is better *for*.)
By contrast, a nihilist might agree that something is "good for" an individual, but deny that this *matters* in any way. That is, they would deny that welfare is good (simpliciter).