From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Zanzo-ken (残像拳, Zanzō-ken; FUNimation "Afterimage Technique"; Literally meaning "Residual Image Fist") is a supportive technique used by many fighters. The user moves so swiftly that an image of the user is left behind. Most often it is used by the user to dodge an incoming attack and get behind their opponent to perform a counter-attack. Its usage is not limited to just counterattacks, though.
Theoretically, this is a move that could be performed (to some degree) in the real world, since it merely requires moving faster than the eye can see. This is a similar phenomenon to that of moving your hand back and forth very fast and seeing a sort of afterimage of your hand. The speed at which the Z Warriors move their entire bodies, however, is far too fast for a normal Human to perform.
 Dragon Ball
Jackie Chun used this attack in the match against Kuririn at the 21st Tenkaichi Tournament. Jackie Chun also performed the Taju Zanzo-ken (多重 残像拳, Tajū Zanzō-ken; Literally meaning "Multiple Afterimage Fist") in which he spun around his opponent and left multiple afterimages of himself. It was hard to tell which was the real Jackie Chun. Goku adapted this technique at the 21st Tenkaichi Tournament and was able to produce even more afterimages than Jackie Chun in an attempt to fool him with his own attack.
Kuririn used the Taju Zanzo-ken once against Goku when they were pitted against each other in the anime, but not in the manga.
Later on, almost every character learned the Zanzo-ken and its usage was not even marked by anything, therefore it met the same destiny as the Flight technique.
It is named the Devil's Afterimage in an early English dub of Dragon Ball, but originally there was no Ma (魔, Ma; Literally meaning "Demon") character that marked all "Demon" techniques.
 Dragon Ball GT
Goku and Vegeta used the Zanzo-ken to distract Omega Shen Long while attempting Fusion in Dragon Ball GT. The two Super Saiyan 4s moved so rapidly that they seemed to "blink" in and out of view and left multiple afterimages. They even managed to move so fast that they performed the Fusion technique in multiple locations at once, greatly confusing Omega.
 Character meaning
- 残 (zan) = residual
- 像 (zō) = image
- 拳 (ken) = fist