Organ (anatomy)An organ is a distinct set of cells within a multicellular organism that perform a distinct function. Organs include the heart, lungs, brain, eye, stomach, spleen, pancreas, kidneys, liver, intestines, uterus, bladder etc. The skin is the largest organ of the human body. The liver is the largest internal organ of the human body.
All organs are made of tissues
Analogous structures exist on the sub-cellular level and are known as organelles.