For beginnerts : a formalism for the description of colloids (i.e. disperse systems).

Let us consider an aqueous solution. This is mostly water. Then let us call it W.
Now some liquid fat : as it is "oil", let us call it O
For a solid : S ; for a gas G.

Now, you can make an emulsion, dispersing oil droplets into the water phase, and you can write it W/O.
The "/" operator means simply "dispersed into".

And of course, they had to be other operators. For example, the coexistence of phases : operator +. Or the inclusion : operator @ (according to IUPAC).
Moreover, you could have to superimpose : operator sigma
Etc.

Now, one can understand easily that using these letters and operators, one can describe more complex systems.

Let us begin with two phases only :
G/G : it is not colloidal, as it is a gas (G/G=G)
G/W : this is a foam
G/W : this is a foam, also, but in oil!
W/O : emulsion
O/W : a different emulsion
W/S : a gel
S/W : a suspension
S1/S2 : a solid suspension
etc : you understand easily, of course.

And it's now very obvious that one can use letters and operators for making formulas, describing more complex systems, such as :

(G+O+W)/S

and so many others...

See more in scientific papers describing this "CDS" formulism.