What skill does the term "FX double lay" refer to?

The term "FX double lay" specifically refers to a double back somersault performed in a layout position. In gymnastics, a layout position means that the gymnast maintains a straight body without any tuck or twist while performing the skills. Therefore, a double back somersault in a layout position consists of two rotations completed in this straight form before landing. This skill showcases the gymnast's ability to manage their body position in the air, emphasizing control and strength. Recognizing the distinctions between the different types of somersaults, such as front vs. back or tucked vs. layout, helps understand the correct terminology and requirements in competitive gymnastics.