Non-refundable credits are credits that only reduces your income liability. If you do not have any income tax payable left on your tax return, you loss any unapplied balance in your non-refundable tax credit. This could be an example of a good tax planning tool that when you want to invest in your RRSP, you need to make sure that first your are using all your non-refundable tax credits.
Refundable tax credits you get as a refund or it paid to you if you are eligible even though you do not have any income tax payable on your tax return.