Spam
Spam is a colloquial phrase that refers to the repeatedly performing an action with no plan beyond hoping a good outcome will happen. While the word itself is the name of a canned meat product, this specific connotation can be traced to a sketch in television series Monty Python's Flying Circus where the word is repeated incessantly, which caused it to gain traction in popular culture as a shorthand for anything repeated to an annoying and harmful degree. In video games, spamming often refers to repeatedly using the same move regardless of it being the optimal play. While a player can spam certain attacks for various reasons, the most common reason is that said move is low risk and high reward with no reason to change strategy. Spamming is most effective for moves with a combination of low lag and 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). While the term "spam" usually refers to attacks, it can also refer to any repeated action at all, such as dodging, edge grabbing, or taunting.
Most forms of spamming tend to be the result of a player's inexperience with their character or the game's mechanics, and thus gravitating towards what seems to work the most consistently. While this strategy can be effective to an extent, hence why attacks are spammed in the first place, spamming often ends up making a player's attack pattern very predictable and easy to counter. Examples of these moves include Kirby's Stone and Pikachu's Thunder. Characters that possess counterattacks, reflectors, or other powerful punish options can usually deal with this type of playstyle, often by spamming said moves right back.
Spamming as a concept is generally not considered harmful to competitive integrity, so tournaments have made very few official rules on the subject. Spam is usually considered cheap when the strategy is exploited and players have difficulty countering and punishing it, though that is typically the extent of the controversy. Some forms of spam are considered important to a character's game plan; juggling an opponent involves spamming the up tilt, up aerial, or up smash of a character (in most cases, the former two). That being said, some techniques considered spamming are genuinely optimal depending on the situation, such as chaingrabbing and planking and wobbling, and as a result often have dedicated rules restricting their usage if not banning them outright. Some moves, like Sheik's forward tilt in Brawl, are ironically easier to spam over time due to stale-move negation drastically reducing their knockback. Using spam as an excuse for losing is usually considered a John.