Fixed-Corner Notation (FCN)
FCN indicates which corner to turn with reference to a fixed corner.
A letter indicates turning that corner clockwise.
A letter followed by an apostrophe indicates turning that corner counter-clockwise.
An x, y, or z indicates rotating the entire cube 90° clockwise about that axis.
An x, y, or z followed by an apostrophe indicates rotating the entire cube 90° counter-clockwise about that axis.