Business casual is more formal than smart casual. For business casual you wear dark trousers or a skirt, a shirt or blouse and possibly a blazer. Closed shoes are standard, a tie isn't required.
Smart casual is freer: coloured trousers are fine, a casual blouse or jumper is fine. Looser shoes are acceptable too. In the Netherlands, business casual is the norm for the office and corporate events. Smart casual suits informal gatherings more. Live Impact advises on the dress code that fits your group of guests.