You can combine two or more slices into a single slice. Photoshop determines the dimensions and position of the resulting slice from the rectangle created by joining the outer edges of the combined slices. If the combined slices are not adjacent or have different proportions or alignments, the newly combined slice may overlap other slices.

The combined slice takes the optimization settings of the first slice in the series of slices you select. A combined slice is always a user slice, regardless of whether the original slices include auto slices.