The Cut Content on this site can be mostly viewed in the StarCraft 2 Map Editor however the definition of Cut Content differs from person to person. In my case it simply means this
Cut content refers to content that is not used (cut) either directly or indirectly in the final version of the game, this also includes any DLC for the game such a Nova Covert Ops & Co-Op
Notice: Some of the abilities/structures/units seen here may have once been cut and reimplemented or were once used and then cut when a patch was released for the game