A magazine holds shells under spring pressure for feeding into the chamber. Some are fixed to the firearm while others are removable.
A cartridge clip has no spring and does not feed shells directly into the chamber. "Clips" hold cartridges in the correct orientation for charging a specific firearm's magazine. Stripper clips allow rounds to be stripped into the magazine while other types are fed along with the shells into the magazine - the M1 Garand operates this way.