Jeans are not business casual. They are suitable for "dress down" days. Appropriate pants for the business casual look are wool, synthetic or flannel pants, khakis or dressy capris.
Bottoms that are not acceptable for business casual include sweatpants, exercise pants, shorts, short skirts, bib overalls, leggings and any tight pants.
For the upper body, tops with collars, including polos and casual shirts, are business casual. Nice turtlenecks and sweaters are proper; however, tank tops, sweat shirts, halters and midriff-baring tops should be avoided. T-shirts are satisfactory if they are plain and worn tucked in under another article of clothing, although they should not have any logos, pictures, words or designs.