Shelving in ordinary English means to put something on a shelf, i.e., metaphorically, to set it aside, take it out of active circulation, store it idle (you "shelve a project").
In quantum optics, a shelving-electron or state is something which disrupts the fast and active dynamical part of an atom and results in intermittency. This was first introduced by Dehmelt in the V configuration[1] (at least according to Ref. [2]).