A torso is the trunk of a human body — minus arms, legs, and head. Anatomically, your torso's job is to protect your internal organs, like your heart, lungs, and kidney, which are all protected by your rib cage.
A statue of a torso in a museum, usually ancient Greek or Roman, is that of the trunk of a human body. These works of art, often carved from marble, are so old that they've frequently lost their arms and heads — but still, the sturdy torso remains. Before the word described an actual human, it meant only "trunk of a statue," from the Greek root thyrsos, "stalk or stem of a plant."