A turtleneck is a type of sweater or shirt with a high collar that folds down and covers most of your neck, kind of like a turtle pulling its head partway into its shell. The collar usually folds over once and fits snugly, keeping your neck warm and protected from cold air.

Turtlenecks became popular in the mid-1900s and are practical for cold weather, since your neck is one of the places where you lose body heat quickly. They're common in winter wardrobes, especially in places with harsh winters. Some people wear turtlenecks under jackets or coats for extra warmth, while others wear them on their own as a complete outfit.

The style is also called a polo neck in some countries. You might see turtlenecks in different thicknesses: thick, cozy ones for outdoor winter activities, or thin ones that people wear indoors or layer under other clothes. While some people love how warm and comfortable turtlenecks feel, others find the snug collar around their neck uncomfortable or restrictive. It's purely a matter of personal preference.