Talk:Slavs/@comment-2405:204:5102:4D8D:358D:8622:9992:8C99-20180827000750/@comment-27810937-20180827090027

It means that every time you build 1 new military building (Barracks, Stable, etc), you gain 5 additional population slots. In the same way you gain population slots by building houses & castles.