A frontstep is a quick motion forward, usually like a hop. It is the forward-moving equivalent to the backstep. There are systems and moves the the same name sometimes.
In Capcom-made games (notably Capcom vs. SNK 2) and NEO·GEO Battle Coliseum, the frontstep is called a “dash”, and the dash is called “run”.
Depending on the game, it may be possible to perform jump attacks and such if the frontstep is actually a hop of sorts. Gallon (Talbain) from the Darkstalkers series, for example, can do this.
In certain KOF installments, you may perform midair command moves (except in ’98 UM) and special moves during a frontstep.
Each character has his or her own greatly varying level of frontstep ability, with speed and distance differing. During a frontstep, one is not only practically defenseless, but also cannot halt it in any way, so it will often get hit.
Accordingly, it isn’t used randomly very often at all, and in ’97 and ’98 gameplay, there are many players who shy away from using it. This is one of the reasons that Extra Mode isn’t very popular. The frontstep does not exist in the series after ’98, but ’98 UM brought it back, along with a walking speed of 1.3 times normal, making the movement efficacies between frontstep and dash about equal.