Business casual would be a Seersucker suit, but it is too early in the year.
I jest - a shirt with a collar that isn't a polo. Not jeans or shorts. Not sneakers. I think that is about the rules. It involves most men conforming into standard american boring chino's and rolled up sleeves on a shirt.
I hate business casual, though I think it works a lot easier for women as they have nice stuff that falls into the category whereas for men it is all really bland. Unless you wear critter pants.