uniform

I'm about to start my training class this Tuesday, the 10th, but there is no given uniform other than business casual shirts and khaki pants. I got the khaki pants part, but what do they mean "business casual" shirt? Not trying to sound stupid, I just have no clue on what to wear.

I'm looking for brand suggestions for a 'Class A' style uniform. Class A for my purposes means standard button up shirt and slacks. No ties, dress jackets, fancy hats etc... just a basic clean and pressed uniform. My employer supplies some absolutely horrible uniforms so I'm looking to upgrade...