4x4 parity occurs on the last layer of a 4x4, where you get a case that is impossible to get on a 3x3 so you need a specific algorithm to solve it.  OLL parity specifically occurs because two adjacent edge pieces are flipped, but generally you can't recognize it until you are at the OLL stage of solving.

OLL Parity Algorithm 1:

This algorithm is the easiest to execute.  It flips the two edge pieces as well as the corners. It also moves other edge pieces in the top layer. If your focus is speedsolving the 4x4 then this is the recommended algorithm. This should be done before you permutate the corners and edges of the last layer.  If you are using CFOP then this is done at the OLL stage, hence the name (OLL Parity).

Rw U2, X, Rw U2, Rw U2 , Rw' U2, Lw U2, Rw' U2, Rw U2, Rw' U2, Rw'

OLL Parity Algorithm 2:

If you have completed your 4x4 solve and you only want to flip the 2 inner edges then you can perform the algorithm below.  It is slower to execute, but will not disturb any other pieces.

r', U2, l, F2, l', F2, r2, U2, r, U2, r', U2, F2, r2, F2

 Rw BOTH Right Layers r INNER Right Layer Uw BOTH Top Layers u INNER Top Layer X Turn the cube clockwise around the X-Axis X' Turn the cube anti-clockwise around the X-axis

Nick

Nice if you forget the parity algorithm every now and then.

Cragmato

@James Havana that’s true.

Jim

Isaac

2nd one helped me with 11×11

Henry

This is great! I’ll have a hard time memorializing it though.

Miles

I loved this for memorizing 4×4 layer by layer

Cc

From this and the pll parity from this web I learned to solve a 4×4 reduction method

timmy

amazing

Tathya

1st 1 works but second doest

AHSAN

thanks !! helped a lot

KD

thank you

J

Helped me solve 4×4!!!

zac

this is amazing! it actually works.

zac

this is amazing! it actually works.

Joe

@jacob If you’re asking how to solve the last corners, than you obviously don’t know how to solve a 3×3. Please go learn 3×3.

Karri

Amrit

This actually helped me

Quin

This actually works!?!!!?!?!??!

this format really helps

jacob

what algorithm do I use to switch the top corners

Viggo

Thanks for the official algorithms

Viggo

Thanks for the official algorithms

Bob

This really does work

Quintin

cool

CM

Very helpful. Thank you so much! Helped me learn 4×4

Akarsh

Last two corners

James Havana

This oll parity algorithm is the most hardest algorithm to memorize