Sephi Yazoo Kadaj

I had considered Immobilize (here) and Stop (here), but the truth is, I’m not sure if both definitions quite suit this:

The subject under Immobilize effect is unable to move, but could still perform other actions, like magic – Sephiroth does nothing (and post-Nibelheim Sephiroth is renowned for being able to use magic without the use of actual Materia).

As far as Stop is concerned, it would be more appropriate than Immobilize, I think, though it’s not like the character here is really trapped in a temporal stasis, at least it doesn’t seem so. We just know all of a sudden he’s completely stunned and not once reacts to Cloud’s strikes.

Now, before Sephiroth stabs Cloud some moments earlier during the fight, Cloud’s Limit is triggered, but according to Wikia he’s going to perform an older version of Omnislash (known as Version 5, whereas the attack shown on the screenshots above is “fanonically” referred as Version 6). Sephiroth was not under the same status he is now, whatever it is, and I think that might be because that older Version 5 is a ‘downgraded’, less powerful one, with one sword only.