Suppose you wants to be able to select a group or set of particles. For example, you want to run a simulation, stop it, select some particles, go back to frame 1, deselect the particles, run the simulation, and then be able to reselect the same set of particles.

You can either use the quick set or a MEL script. In MEL, you can do the following:

//Saves current selection for later use.

 string $selectionSet[];

 $selectionSet = `ls -sl`;

 //Recalls saved selection.

 select -r $selectionSet;