Final answer:
The Double Hardflip is a complex skateboarding trick involving two rotations of the board while the skateboarder flips it both vertically and horizontally in the air.
Step-by-step explanation:
The Double Hardflip is a skateboarding trick where a skateboarder performs a combination of a hardflip, which is flipping the board vertically and horizontally underfoot while in mid-air, with an additional rotation that causes the board to flip over twice.
It requires significant skill, coordination, and timing, as the skater must catch the board with their feet after it has completed two flips and before landing on it. This trick is a variation of the basic hardflip and is considered quite advanced due to the required precise control over the skateboard.