The term originally referred to nail extensions made using a hard gel product hardened by curing under an ultraviolet or L.E.D. (light emitting diode) light.
However, recent use of the phrase includes many nail services involving the use of gel products, including the very popular gel polish manicure.
Gel nails are very similar to standard acrylic nails.
You can paint, wear french tips and airbrush designs on both types of artificial nails.