Shirts, blouses, and tunics are all tops women frequently wear, and each piece is subtly different from the other, with wide variations in its category.
A shirt is a simple top, usually pulled over the head—as with a t-shirt and many sweatshirts--or buttoned up the front, with a hem typically reaching above the waist.
Though people often use the terms shirt and blouse interchangeably, the two styles do have a distinct difference. Women's blouses resemble shirts in most ways, but blouses tend to fit more loosely and have a dressier look.
A tunic is much like a blouse in its loose fit, but a tunic's hem reaches between the hips and the knees. Some tunics pull over the head; others button up the front or even the sides. Open tunics, very similar to open cardigans, make a wonderful top layer over a blouse or a shirt, adding a stylish flow to your outfit.