How do you define osmos?

I think you're looking for osmosis.

Osmosis is a kind of method where substances used to flow from a place to another. Osmosis is where water molecules flow from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.

A partially permeable membrane means that membrane can select what can go through or not. Also, osmosis must be the flow of water, nothing else.