Magnet wires are copper wires with a thinner enameled insulation layer, rather than the usual thicker plastics, and are often called enameled copper wires.
You can use ordinary copper wire with plastic insulation, but the winding has the most turns. It will work, but it is not efficient.
The conductivity of the two wires is the same, but the electromagnetic copper wire is specially coated with a thin and high heat-absorbing material. Thin insulating material helps to form more turns in a shorter area (in motors, transformers, relays, etc.) and can absorb heat. Ordinary copper wire is insulated with thicker materials and may require more area to wind more turns. Therefore, the winding will not work effectively and will melt the insulation in the heat.
Magnet wires are coated with enamel insulation instead of plastic or rubber coating. This makes the insulating layer thinner and allows a more compact winding, which makes the magnetic field in the coil denser.
Magnet wire also has a thinner wire gauge (thickness), which is a comparison between solid wire and conventional wire. The latter has a larger size and uses a stranded wire form.
Rectangular Enameled Copper Wire is also the main copper wire, welcome to consult and purchase.