This is an action-related message of the AbuseFilter extension.
abusefilter-action-*messages are shown on the main Special:AbuseFilter page in a column. They're short descriptions of what a filter does. They can be nouns or noun sentences, or verbs which have the AbuseFilter as subject.
abusefilter-edit-action-*messages are shown on the page of each filter, next to the checkbox through which the privileged user can "order" the filter to take that action, so it's usually best translated with an imperative or other verb sentence.
Revoking auto-promoted groups
To block autopromote means that actions matching the filter will cause the user in question to be barred from receiving any extra groups from $wgAutoPromote for a period ranging from 3 to 7 days (random). Additional information available: https://www.mediawiki.org/wiki/Extension:AbuseFilter/Actions