Eps 1 through 24 of the third season exist only as episode synopsis on the site http://sr.kc.kodansha.co.jp/onair.html
They've recently 'aired' ep 12.
25 and 26 are being released with special editions of manga vols 21 and 22.
Really, it's a way for them to have an OVA to cover the end of the series without having to do anything about the stuff that happened between season 2 and the end point.
So yeah "3rd term" = 2 OVAs covering the end of the series.