What does the medical terminology combining form sub- mean?

Hypo- means low or below.
Below or less than
Below or less than
hypo is a prefix indicating low. It will be used with other Words llike hypoglycemia-low blood sugar or hypocalcemia-low calcium.
Under, below; e.g., "hypodermic" means "below the skin."
"to enter" such as a "hypodermic needle"