What is the difference between organ and organelle?

An Organ and organelle are two different structural units that are highly specialized in order to perform unique functions at different scales and in different locations.

Organs exist exclusively in higher organisms such as animals and plants. An organelle can be thought of as the functional analogue to an organ, in cells within the body and single celled organisms like bacteria.

Given this difference in size scales, organs are therefore macroscopic structures, while organelles are structurally microscopic. The primary difference between an organ and an organelle is their organization and composition.