What is sub meaning?

Sub is a prefix that means "below" or "under." It is commonly used in words to indicate something that is secondary or subordinate in nature, or that is located below or beneath something else. For example, submarine means a vehicle that operates below the surface of the water, and subculture refers to a smaller or lesser-known group within a larger culture. The prefix sub can also indicate the opposite of something, such as subzero meaning temperatures that are below zero degrees Fahrenheit.