What describes something that happens as a pilot get closer to the speed of sound?

As a pilot approaches the speed of sound, they experience a phenomenon known as compressibility, where air density increases and pressure changes occur significantly. This is accompanied by the onset of shock waves and potential control difficulties, leading to a critical point known as transonic flight. The aircraft may also encounter a marked increase in drag, often referred to as "drag rise," as it nears the speed of sound, which can impact performance and stability.