A Clapton coil gets its name from the fact that the wire’s structure is a lot like that of a guitar string. Most coils are made from single strands of kanthal, but Clapton coils are more complicated. They have a thinner, higher-gauge strand of wire wound tightly around a thicker, lower-gauge core. The wire looks just like a guitar string from the outside, but just constructed from kanthal.
The biggest advantage of using Clapton wire in your RTA or RDA build is that it increases the surface area of the coil in comparison to ordinary wire without increasing the resistance too much. The more surface area there is to get hot, the more e-juice you will vaporize when you press the fire button. This means that the Clapton coil approach is generally better for both vapor production and flavor than a similar coil made from ordinary wire.