A small muscle in the upper arm that originates on the Coracoid process (Crazy, right?) and inserts around the upper-third of the Humerus.
But more importantly, A muscle that you will rarely if ever see/hear mentioned when looking up exercise routines online, reading body-building forums, or when engaging in casual conversation at your local gym. Why? Because very few meathead Broscientists ever have enough actual scientific evidence or basic anatomical education to ever know what the Coracobrachialis muscle is, let alone spell/pronounce it.
This neglected muscle falls unfortunately under the same category as other never talked about/trained yet just as important muscles such as Anterior Tibialis, Levator Scapulae, Teres Major (or Upper Lat, as many non-educated Broscientists will tell you, despite it being an entirely different muscle than the Latissimus Dorsi) and Anconeus. (That's right, your arm IS made up of more than just the Bi's N' Tri's.
Educated person - "Hey man, what are you workin' out today?
Local Broscientist - "Well, ima prolly hit the bi's N' tri's pretty hard, maybe do some Lats, Pecs, Traps, you know, all the important muscles."
Educated person - "That sounds.... Awesome.. You ever tried training your Coracobrachialis?"
Local Broscientist - "uhhhhh.... you mean Pecs?"
Educated person - "Uhhh yeah..:\"