The difference between them is lies in formality and structure: T-shirts are casual, usually made of stretchy knit fabric with no collar, while shirts are more formal with a collared, button-up design that provides a more formal silhouette.

A T-shirt (also spelled tee shirt, or tee for short) is a style of fabric shirt named after the T shape of its body and sleeves. Traditionally, it has short sleeves and a round neckline, known as a crew neck, which lacks a collar.

: a garment for the upper part of the body: such as. a. : a cloth garment usually having a collar, sleeves, a front opening, and a tail long enough to be tucked inside trousers or a skirt. b. : undershirt.

Most dictionaries recommend T-shirt, and it is the form most common in edited writing throughout the English-speaking world.