It is known by both names.
The Union name was Bull Run; the Confederate name was Manassas.
The Union named its battles after natural features(Bull Run was a stream) while Confederates named theirs after towns or place names.
https://www.history.com/news/why-do-some-civil-war-battles-have-two-names
@SayWhenLA 25m25 minutes ago
Surprise, surprise! These people are nauseatingly evil. James Baker is good friends with @DavidCornDC... first "journalist" to report on Steele dossier. Their kids carpool together! &...Baker is the SUBJECT of a CRIMINAL LEAK investigation. Whole thing is blowing wide open 🍿🍿🍿