Currently, when rep is changed due to the removal of another user account (to undo the rep gain/loss that happened when they up-/down-voted/accepted/were downvoted by you), the associated message is simply "User was removed". I am not the only one who found that message rather cryptic (I had to go search meta when I saw it, and I found my answer in a duplicate, so that makes me at least the 3rd person to not understand it).
I think it's a good idea to add a link to the relevant meta answer or some more descriptive text to that.
Another user was removed; reputation changes linked to the user's activity were reverted.
(I can see how it's hard to fully explain the event succinctly, that's why a "what is this?" link to meta or an FAQ question/answer might be better.)