Barrier Skip is the theory of getting to Ganon's Tower without breaking down the Hyrule Barrier. It is possible to skip the barrier by unloading it, but before that was found there were many theories for getting past it early.
In this picture, the pink area represents the edge of the knockback region. Everywhere inside can be freely walked around. Slightly behind that is the physical barrier. The physical barrier has no top. Touching the knockback region causes Link to be knocked back. This knockback can be temporarily canceled by pulling out the Wind Waker on the same frame that you stop blinking from getting damaged, or knocked back. The knockback gets re-enabled if you take damage or leave the knockback region.
On the japanese version, the only trigger needed to break the barrier is watching the Hyrule 3 electrical barrier cutscene going off. On the US/PAL versions, you also need the fully charged master sword.
That electrical barrier cutscene requires many triggers, which are:
1) Zombie Hover: The barrier extends so far up, that there is not enough horizontal space to get enough height to reach the top. Even if you got to the top, you would be knocked back because it is within the knockback zone.
2) Zombie Hover inside the damage field: In order to Zombie Hover, you need to take damage so you can have 0 hearts. Taking damage re-enables the knockback. To cancel it again, you need to stop blinking first, but you die before you are able to. Furthermore, nothing we have access to in Hyrule can allow disabling the knockback barrier while zombie hovering (stored text doesn't work).
3) There is no way to clip through. The railing does not allow you to hang from it, so a ledge clip is not possible. With 35 speed or more you could clip through the seam where the 2 invisible walls meet, but the maximum speed available is 26.
4) Wind Waker Dive, then Zombie Hover: you can't have cancelled the barrier and be dead at the same time, because you are still blinking when performing a zero heart wind waker dive.
5) Deku leaf: After the Wind Waker dive, you could use the deku leaf, but you are far too low and there is nothing to land on.
6) Using the death cutscene to cancel the knockback barrier: for some reason, even if you cancel the knockback barrier with the death cutscene, getting control back reenables the knockback.