@noelle a bit of both; the ActivityStreams concept is “Flag”: https://www.w3.org/TR/activitystreams-vocabulary/#dfn-flag
a “report” in mastodon is a “Flag” sent by an instance actor to the… inbox of the reported user? if i’m reading these specs correctly?
@noelle these semantics aren’t defined in ActivityPub; they’re a consensus interpretation by some AP servers