The hairstyle where hair is shaved or clipped very short is called a buzz cut.
A buzz cut is generally made with electric or manual hair clippers, leaving hair at a short, fairly uniform length. The name comes from the buzzing sound of the clippers. Some versions leave the same length across the head, while others taper the sides or vary the length on top.
The style became more widespread in the late 19th century after Serbian inventor Nikola Bizumić developed improved manual clippers. Buzz cuts were practical wherever grooming had to be quick and consistent, including military training. Armed forces also valued them for easier maintenance, cooling, uniformity, and historically, reducing opportunities for head-lice transmission.
A buzz cut is not exactly the same as a shaved head: clippers usually leave visible stubble, while a razor can remove hair down to the skin. A crew cut is a related but distinct style, typically leaving the hair on top longer. Quiffs and pompadours, by contrast, depend on height and styling rather than extremely short clipping.