Something that was much insisted on when I was at school, because i guess some kids found it hard to get their heads round. Like 1M HCl or NaOH are 1N but 1M H2SO4 or Na2CO3 are 2N. You get the idea? - it's the same as the distinction between molar masses and equivalent masses (or weights as we used to call them).
I think they have been phased out of teaching now, have they? If so it's no loss, they are unnecessary.