Literally it means to the point of nausea (that is feeling sick). So something that has been done ad nauseam is something that has been done so extensively or so often that everyone is sick of it.
She went on and on ad nauseam about her divorce.
Let's stop this discussion about equal rights. We've been debating about this topic ad nauseam
I wish the meeting would come to a decision, we have been discussing the topic ad nauseam
Both are correct.