i'd say that consent is agreeing to something when one believes one has the option to not-agree to it.
there are limitations to that definition, including that to believe one has an option, one must have already imagined alternatives, ie, my definition puts a lot of responsibility on the individual consenting or not-consenting. that might or might not be fair/appropriate/reasonable in every situation. but what definition *is* good for every situation?
work is the most obvious example, i think, but for many people drugs, sex, capitalist interactions of various sorts, abusive relationships, are all in the conversation as well.