Most things that can't be moved on Shabas (or yom tov) can be moved if the following two criteria hold:
- One is moving them by means of another object.
- The purpose of moving them is not for their own sake but for the sake of some permitted object.
An example frequently given is leftover crumbs on a table. If they can't permissibly be moved by hand (as is sometimes the case) then they can nonetheless be swept up with a squeegee or knife, so long as the purpose is a clean table rather than collecting the crumbs. (Note, though, that the rules are more complicated than I can include here and, in particular, not everyone agrees that the case of crumbs on a table falls under this exemption. As always, consult your rabbi with any practical questions.)
Why is it called that? Moving something via another object doesn't make the motion more "from the side". Does it mean you're moving the object from your side? But you always move things from your side, as your hands are on your sides. Or does it perhaps mean you're moving the object from its side? But using another object instead of your hand doesn't mean you're approaching the forbidden object from any particular side. Or what does it mean? What's the understanding of this phrase as applied to this permitted action?