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.

An A-shirt. A sleeveless undershirt, also known as an A-shirt, tank top, has large armholes, a large neck hole, and offers little protection for armpit sweat. A crew neck T-shirt has a high neckline, often requiring fully buttoned shirts to avoid being seen. A V-neck T-shirt has a V-shaped neckline.