“Life is good especially on a Friday.” —Anonymous
This is different for every company that is why you should rely on corporate policy when choosing your outfit.
Know the Corporate Policy
Casual Friday means something different for every company. Researching company policy is helpful when you are starting out at a company along with observing what others wear when Friday rolls around. If your company tends to be on the more business professional side Monday-Thursday you can expect Fridays to be more business casual rather than what is considered "casual Friday". On the other hand if your company is more casual on other days you may be able to wear jeans.
What to Wear
Dark wash jeans without rips
Fitted shirts or button-down blouses with blazer
1-1/2 inch peep-toe pumps