Spike

A Spike is a type of attack in Super Smash Bros. and Melee that sends the opponent downward until the hitstun wears off. A Spike is not to be confused with a Meteor Smash, which also sends the opponent downward, but can be Meteor Canceled before the hitstun wears. There are no true Spikes in Brawl, only Meteor Smashes, as all attacks that deal downward knockback can be Meteor Canceled - however, Meteor Smashes can't be canceled immediately so they are still very useful for finishing off opponents. When referring to Brawl, people often use the terms "spike" and "meteor smash" interchangeably.

In Melee, there were two primary differences between meteor smashes and spikes. The main difference of the definition is that meteor smashes can be meteor canceled while spikes cannot, since the game doesn't register them as meteor smashes. The second difference is that all meteor smashes in Melee send opponents straight down or straight up (depends if they're airborne or grounded) while spikes send opponents at an diagonal angle that is downwards on airborne opponents or upwards on grounded opponents. While spikes under the true definition do not exist in Brawl, the meteors that were spikes in Melee send opponents at an diagonal angle still (though the trajectory is not as diagonal as it was in Melee).

Spikes are not guaranteed KOs - if the opponent's damage is very low, the Spike will be too weak to put them so far below the stage that they can't get back. However, they tend to be extremely effective KO moves - recovery from most Spikes tends to be impossible at damages near or above 40%. Because of this, many smashers (particularly those who main characters with good Spikes, like Falco, Ganondorf, and Marth) try to integrate Spikes into play as often as possible.

In Super Smash Bros.
Since there is no Meteor Canceling in the original Super Smash Bros., all attacks that deal downward knockback are considered Spikes.
 * Captain Falcon - Down aerial
 * Donkey Kong - Forward aerial and Down aerial
 * Kirby - Down aerial and Final Cutter
 * Mario - Mario Tornado (if the opponent's head is in contact with Mario's feet during the end of the animation)
 * Ness - Down aerial
 * Samus - Down aerial
 * Yoshi - Forward aerial and Down aerial

In Super Smash Bros. Melee
With the introduction of Meteor Canceling in Melee, most attacks with downward knockback are in fact Meteor Smashes - in fact, only six characters are known to have true Spikes:
 * Captain Falcon - Nipple spike (when the opponent is hit with the upper half of his body during his Down aerial)
 * Falco - Down aerial
 * Ganondorf - his Down Special Move, Wizard's Foot (if used in the air)
 * Marth - Down aerial tip(NTSC only)
 * Roy - Up Smash (if an airborne opponent is hit with the tip of the sword)
 * Fox -Down aerial (Even though it is a spike, it's mostly impractical as it produces no knockback except on lower handicapped opponents).