Business Casual at most corporations means that a man may wear a less formal shirt such as a button down cotton shirt or even a collared golf shirt. He may wear a slack that is not part of a suit, but that would be appropriate to wear with a sport coat. He may also choose to wear a sport coat. A tie is not necessary for business casual.

My son Randy and his wife Melissa met us for dinner last summer, after a casual Friday day at the office.
For a summer business casual look, the man may wear a collared knit shirt with cotton or linen slacks. A sport coat is not necessary for a business casual look in the summer. The woman may wear slacks with a blouse or a summer dress to the office. She may also wear a skirt, either long or reasonably short, and combine it with a blouse.

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