Spam
Spam refers to the use of a certain move by any character that is repetitively being used, be it a ground attack or a projectile, the latter being most commonly spammed. Spamming is more effective for moves with a combination of low lag and decent to long range (such as a fair amount of forward tilts), as well as those with fast repeating hit rate (such as Fox's Blaster from Melee onward). This action is usually considered cheap when players have difficulty countering it. Juggling an opponent involves spamming the up tilt, up aerial, or up smash of a character (in most cases, the former two). While the game discourages spamming with stale-move negation, the point of spam is to throw out many attacks to the point where the reduced damage can be made up simply by using the move twice as much, and in Brawl, some moves like Sheik's forward tilt are even easier to spam due to stale-move negation drastically reducing their knockback.
Most forms of spamming tend to be the consequence of a player's inexperience with their character or the game's mechanics, and often end up making a player's attack pattern very predictable and easier to counter; playing with characters that have counterattacks, reflectors or powerful punish options is often a good way to deal with this kind of spam. However, some techniques used in high level play such as chaingrabbing and planking are also occasionally considered a form of spamming. Using spam as an excuse for losing is usually considered a John.
