diaphragm
No, it is not. It is the large chest muscle.
Pectorals
It's called - the diaphragm (pronounced di-a-fram)
diaphragm
Yes it is.
m. teres minor and major
The heart you idiot!
Pectoralis major
the diaphram
This only happens with men who have large pecs (chest muscle pectoralis) The muscle tucks a man's breastskin under it which gives it a manly look. Some men can produce milk and some men end up squirting milk under their chest because their nipple gets squashed.
Exercise exercise exercise! If fat loss if your goal, then cardiovascular activity is absolutely essential. You will lose over all fat, including chest fat, if you do cardio. You can and should incorporate weight training, particularly for large muscle areas like legs, because the more muscle you have the more overall fat you will burn. Obviously doing chest exercises will help tone the muscles in your chest as well, but it is a myth that spot targeting an area will increase FAT loss in that area. It's just not true.
The gluteal muscle.