A smash attack is an attack performed by "tapping" (quickly tilting) the control stick and pressing the A button at the same time. This class of attacks includes forward smash, up smash and down smash. Smash attacks generally have the highest knockback of the moves in a character's arsenal, with the forward smash usually being the most powerful. In Melee, Brawl, and Smash 4, they can be charged by holding the A button down, then releasing when you want the attack to unleash, thus giving it more damage and knockback. A smash attack can be charged for exactly 60 frames, or 1 second. A fully-charged smash attack does 1.4x damage; for example a smash attack that normally does 16% damage will do 22.4% damage when fully charged.
In Melee's Versus mode, smashes can also be performed by pressing the C-stick in any direction. Holding the Z button while pressing the C-stick results in charging the smash. Some forward smashes can be angled in the same way forward tilts can - depending on the angle and the attack, a different amount of damage may be dealt. Usually, smash attacks deal extra damage when angled up and less when angled down (usually a 1% or 2% difference), which the tradeoff being the difficulty in hitting shorter targets when angled up. Angled smash attacks can have other properties as well, such as Luigi's forward smash gaining extra IASA frames when angled up.
In Super Smash Bros. Brawl, one can play the game with 4 different controller setups. While the Wii Remote, the Wii Remote and the Nunchuk, GameCube Controller, and the Classic Controller all have control sticks to perform Smash attacks the standard way, when using the Wii Controller on its side, one can press the direction they are attacking and press both the 1 and 2 buttons at the same time instead. When attacks are charged in Brawl, characters now move while flashing as opposed to just freezing then unleashing the attack. In addition, a small sound can be heard when charging a smash attack. For most characters it's a 'crack' sound, however certain smaller or "anthropomorphic-like" characters like Yoshi, Diddy Kong, Kirby, and Pikachu make a different squeaky noise instead.
Smash attacks are often powerful finishing moves, but they are usually slower than neutral or tilted A attacks, and have a longer lag. A character who overuses smash attacks is easy to counter. The smash attack's power will also be affected with Stale-Move Negation when it is overused.