Triceps: The muscle that extends (straightens) the forearm. The triceps can be felt as the tense muscle in the back of the upper arm while one is doing push-ups. The triceps has three heads, or origins. Its full name is the triceps brachii. QUESTION What causes tooth decay? See Answer From Healthy Resources 10 Rheumatoid Arthritis SymptomsWhat Is Exocrine Pancreatic Insufficiency? Featured Centers Good and Bad Foods for PsoriasisVideo: Getting Personal on Life With MS Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19