The Deflicker is a setting in Super Smash Bros. Melee and Brawl that is found under options. It adjusts the way the screen appears when the game is played. When deflicker is turned off, less blurring is applied to the edges of objects, causing a sharper appearance, at the cost of featuring more jagged lines ("jaggies"). When deflicker is instead turned on, more blurring is applied to edges, giving a slightly blurrier look to the game while also removing most of the jagged lines.
In Brawl's NTSC release, the menu option for the Deflicker is a capital letter D overlaid on several straight lines; in the PAL release, however, the D was replaced by a circle, as to reflect the various languages of the game.