What does the prefix "sub" mean in medical terminology?

The prefix "sub" in medical terminology means "below" or "under." This prefix is commonly used in various medical terms to indicate a position that is lower than or beneath something else. For example, "subcutaneous" refers to the layer of tissue located under the skin, while "subdural" describes a space beneath the outer membrane of the brain. Understanding the meaning of prefixes like "sub" is crucial for interpreting medical terms accurately, as it helps in understanding the relationship and location of anatomical structures or conditions in the body.