Mass-volume percentage definition
Mass-volume (or weight-volume) percentage (% w/v) is defined as
So for example solution containing 5g of substance in 100mL is 5% w/v.
Two things are worth noting here. First, mass-volume percentage is expressed not in % units, but in [% g/mL]. Second, due to the way this concentration type is defined it is possible to have solutions of concentration above 100% w/v - see concentration follies for an example.