A DACUS (Dash Attack Canceled Up-Smash) is when a character intiates a dash attack and immediately inputs an up smash right after the dash attack. Although this takes practice to do consistently, it is easiest to do on the GameCube controller, although it's easy to consistently do a DACUS with Snake with the Wii Remote and Nunchuk.
When a DACUS is initiated, the character will slide across the stage (quicker than if he was dashing or walking) while doing an up smash or charging an up smash. This is most notable with Snake as he slides approximately 3/4 of the way across Final Destination with his DACUS.
Characters that can noticeably DACUS:
To do a DACUS on the GameCube controller, the most well-known and/or easiest way is to initiate a dash, push down on the C-stick to start the dash attack and press up on the control stick and press Z at the same time to cancel into an up smash. Another method involves using R instead of Z if R is set to attack.
When using Snake and the wii remote/nunchuk controllers, doing a dash attack and immediately initiating an up smash quickly enough will cause him to slide across the stage and DACUS, although the two actions need to be done extremely quick.