The word is "casual" (you transposed two letters). It's pronounced "CAZH-wal." "Casual" means "informal." "Hi" is a casual greeting, "Good morning" is a formal greeting. "Formal dress" means the kind you would wear in a formal, dignified situation. In the United States, at a formal occasion, I would wear a "business suit" with a jacket and tie. "Casual" means everyday clothing you might wear for going to the supermarket, or playing outdoors with your kids. "Nothing too casual" is unhelpful! That's a badly written dress code! It means "casual, but not too casual." In real life, it is perfectly appropriate to ask your human resources department specific questions. They want people to follow the dress code, and will be happy that people are asking questions about it. For example, maybe blue jeans are acceptable if they are fairly new, clean, and modest. Maybe the kind of blue jeans that are made to look worn out, old, and shabby--with holes and rips in them--are "too casual." ("Causal" is a completely different word. It's pronounced "caws-ul" and it means "having a cause-and-effect relationship.")

It really depends on the context. In many work settings, a T-shirt and jeans would be considered "too casual" (you should wear a dress shirt and dress pants). In other work settings, though, a T-shirt and jeans would be fine, but a T-shirt and shorts might be considered "too casual." If you're not sure what they mean, the safest answer is to wear dress clothing (but not something highly formal).