Slices through the mesh or selected faces creating new edges using a plane defined by two points in screen space, perpendicular to the current view.  Slice typically picks points on either side of the mesh to define the slice.

Select by Angle

Select by angle selects all faces adjacent to a selected face within a given angle of the original face.  The first two images below show selection with an angle of zero.  The third image shows an angle of 40 degrees.

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