What is what size is youth medium?

Youth medium clothing sizes vary significantly depending on the brand, manufacturer, and even the specific garment (a youth medium t-shirt will likely be different from a youth medium jacket). There's no single, universally accepted standard.

However, generally speaking, a youth medium is intended for children in the approximate age range of 10-12 years old. The corresponding measurements would typically fall somewhere between children's sizes Large and Small.

To get the most accurate size information, you should always refer to the specific size chart provided by the retailer or brand. These charts will give you the actual chest, waist, hip, inseam, and other relevant measurements for that particular youth medium item. Don't rely solely on the "youth medium" label.