What's the difference between SKYACTIV and SKYACTIV-G?

What's the difference between SKYACTIV and SKYACTIV-G?

The SKYACTIV-X engine uses a spark to ignite only a small, dense amount of the fuel-air mix in the cylinder. ... Ten to 30 percent more torque than the current SKYACTIV-G gasoline engine with better fuel efficiency than the current SKYACTIV-D, and a power increase of ten percent.