This specifies whether the move is 2 or 3 axis and when the move takes place.
3D
The move follows the complete 3 axis vector specified by the move type (normal, tangent, tangent+angle, or fixed).
2D
The 3 axis move is calculated and then flattened to go in the same direction as the 3 axis vector, but with no Z motion. This is useful in undercut situations.
Undercut 3D
As above, the move follows the complete 3 axis vector specified by the move type. The move will only be used if the surface is undercut with respect to the cutting view at the point of the leadin or leadout move.
Undercut 2D
As above, the 3 axis move is calculated and then flattened to go in the same direction as the 3 axis vector, but with no Z motion. The move will only be used if the surface is undercut with respect to the cutting view at the point of the leadin or leadout move.