What "begin to flake" means in the context of sauteing a fish? I encountered 


  When you see the bottom of the fish fillets turn opaque, tilt the pan and, using a large spoon, baste the tops of the fish with the hot oil. Do this constantly until the top of the fillets begin to flake, about 3 minutes.


in a recipe. It is unclear to me what it means. For example in https://en.wiktionary.org/wiki/flake closest to this use is "To break or chip off in a flake" what seems to make no sense - especially as recipe explicitly mentions "preventing your fish from falling apart". Example images in recipe also display the fillet in one part, without small parts separated away.

What is the meaning of "begin to flake" in this context?

relevant recipe: http://www.simplyrecipes.com/recipes/cod_sauteed_in_olive_oil_with_fresh_tomatoes/
When the fish cooks, the meat will start turning opaque; at one point, you will see that the fish will start to "split" into flakes or layers.

see this video (at about 2:15 and onward) you start to see layers in the fish.

https://www.youtube.com/watch?v=gluRaUv88sk

For example in the following video, you see the salmon has "layers" of fat and meat; when the meat is just right, the layers will be easily "flaked" when the fish is cooked.

https://www.youtube.com/watch?v=3KLQnGS1TjQ