A louver ( American English ) or louvre ( British English ) , from the French l'ouvert ; `` the open one '' ) is a window , blind or shutter with horizontal or , less often , vertical slats . They are angled to allow light and air in . A louver ( American English ) or louvre ( British English ) , from the French l'ouvert ; `` the open one '' ) is a window , blind or shutter with horizontal slats that are angled to admit light and air , but to keep out rain , direct sunshine , and noise .