Cathode rays are streams of electrons that are emitted from the negative electrode, or cathode, in a vacuum tube. When an electric current passes through the tube, these electrons travel towards the positive electrode, or anode. The behavior of cathode rays can be influenced by electric and magnetic fields, demonstrating their charged nature. Discovered in the late 19th century, cathode rays played a crucial role in the development of atomic theory and the understanding of atoms. They were instrumental in the discovery of the electron by physicist J.J. Thomson, leading to significant advancements in physics and chemistry.