The term "20mm rounds" refers to ammunition that has a diameter of 20 millimeters. These rounds are commonly used in various military applications, including aircraft cannons and anti-aircraft systems. The size allows for a balance between firepower and manageable recoil, making them effective for targeting both ground and aerial threats. 20mm rounds can be found in different types, such as armor-piercing and high-explosive variants. They are typically fired from weapons like the M61 Vulcan or the Oerlikon GSh-6-30K. Their versatility and effectiveness make them a crucial component in modern warfare.