If something is stylized it means it's represented in a non-naturalistic conventional form. The heart-shaped symbol in the popular phrase "I heart NY," for example, is a classic stylized representation of a real heart.
Anything can be stylized — an entire movie or play or wardrobe, for example. Superhero movies that make entire cities look like cartoons are stylized. The film director Elia Kazan summed up the difference between what is stylized and what is not nicely: "Stylized acting and direction is to realistic acting and direction as poetry is to prose." From the Old English word stile meaning "designation, title, manner or mode of expression."
