Informal shirts are a type of clothing that is typically worn in casual settings. The two most common types of informal shirts are tees and polos. Tees, also known as t-shirts, are short-sleeved, collarless shirts that usually have a design or logo printed on them. Polos, on the other hand, are collared shirts with short sleeves and usually have two or three buttons at the neckline. Both tees and polos are popular choices for casual wear and can be found in a variety of colors and styles.