The spleen is an organ that's about the size of a fist, located on the left side, just below the ribcage. Don't let its small size fool you. This little organ is very important in helping the body fight infection.
The spleen is responsible for removing old red blood cells and producing and storing a reserve of blood in case the body needs it. It's a little organ, measuring little more than four inches in length. The term "vent your spleen" is one you might see used. It means to vent your anger, as spleen is another word for bad temper or spite.