It seems to be generally agreed that a foundationalist view of any area of justified beliefs is the affirmation that there are some (basic) beliefs which are to some degree credible for a person independently of reflection on logical relations to any others of his beliefs, and that any other beliefs of his are justified because of appropriate logical relations to these basic beliefs — thus contrary to the coherentist thesis that beliefs can only be justified by appeal to their relation to other beliefs of a person, independently of whether these other beliefs are themselves independently credible. Thus, for the area of moral beliefs, foundationalism is the view that there is at least a subset of a person's moral beliefs which are either justified independently of logical relations to any other beliefs, or are justified by their logical relations to some other beliefs, either independently credible moral beliefs, or independently credible non-moral ones.
I am here restricting ‘ethical’ beliefs to moral beliefs, as distinct from beliefs that something is a good thing or intrinsically good or good for a person.