"Flash" (stylized as FLAϟH) is the debut single by South Korean boy band X1, released on August 27, 2019 by Swing Entertainment as the lead single from their debut extended play (EP) Emergency: Quantum Leap.

The dynamic single flits between tempos, starting sleek before speeding up to vibrant pace, only to veer this way and that in the run up to the frenzied chorus and a dramatic beat drop.

As much of a display of the members' vocals and rapping prowess as it is a performance-based song, "Flash" is a pure audio-visual experience meant to be simultaneously observed and listened to through the track's music video, during which X1's pristine, and aggressively impassioned, choreography takes center stage as they take a quantum leap towards the future of their career.

[3] It also became the fastest K-pop boy group debut music video to reach 100 million views, beating the record set by TXT's "Crown".

[6] They won their first music trophy on SBS MTV's The Show on September 3 and became the fastest boy group to receive a music show win taking only 5 days to do so beating the record set by WINNER's "Color Ring".