OAV is one of those old terms that denotes a video that skipped movie theaters and television and went straight to video (like VHS tapes and then disc based media later) back before the days of streaming, so you could think of scheduled streams as being like television- sometimes this format is called linear and the recordings of these streams are called video on demand or VODs.

So, most anime platforms have a scheduled release of videos that are more or less synchronized with TV releases, so it’s easier to think of those VODs as TV and the videos that are not broadcast are OAVs because typically they are packaged as extra material in DVDs.