What does "subcutaneous" mean in medical terminology?

Subcutaneous means beneath the skin, from sub meaning under and cutaneous meaning relating to the skin. Subcutaneous tissue, also called the hypodermis, is the deepest layer of skin composed primarily of fat and connective tissue. Subcutaneous injections deliver medication into this fatty layer, providing slower absorption than intramuscular or intravenous routes. Common subcutaneous medications include insulin, heparin, and some vaccines.