What the hell are the Solaris slices

When I tried to get a dd-mirror of a complete disk running under Solaris, I had the problem how to find out how to do this with these strange solaris slices (that also always confuse me when I set up a Solaris machine). But the online Solaris documentation (docs.sun.com, very good, always worth the look) had the right answer:
slice 2:
refers to the entire disk, by convention. This slice is defined
automatically by the format utility and the Solaris installation
programs. The size of this slice should not be changed.
The meaning of all slices can also be found in the SUN online documentation