nonbinary: identifies in any way that falls outside the woman/man gender paradigm. this includes but is not limited to agender people, and some other examples are genderfluid, bigender, and xenogender identities
agender: lacks gender entirely or does not identify with any particular gender
so all agender people are nonbinary, but not all nonbinary people are agender
my understanding is that:
so all agender people are nonbinary, but not all nonbinary people are agender
i had to look that up, and i’m rather happy there’s a word for that now.