Bore size refers to the internal diameter of the trumpet's tubing, typically categorized as small, medium (medium-large is most common), and large bore. A smaller bore offers less air resistance, making it easier to play with a brighter, more focused sound, often favored by lead and commercial players. A larger bore requires more air support but rewards it with a broader, darker, more powerful tone favored in orchestral and classical settings. Medium-large bore instruments are the versatile default recommended for most students and general use, since they don't demand the extra air support a large bore requires before a player has developed strong breath control.