Broken is a term used in many games, particularly fighting or otherwise competitive ones, to describe characters, techniques or other elements or combinations of element so overpowered that they severely skew the game's balance in their favor, making alternatives nearly irrelevant by comparison.
A classic example in the Super Smash Bros. series is Fox when the fight occurs in Hyrule Temple in Melee: he can outrun almost every other character on the massive stage, and can chip at the enemy by using his Blaster to fire shots, allowing him to easily time out a match and win by percentage. This type of strategy is almost always deemed "broken" and action is taken (in this example, banning Temple from tournament legal stages) to prevent it from impacting competitive play. The definition is, by nature, subjective, so what is generally considered broken often changes as the competitive community evolves, particularly after the release on a new game. Despite this, broken elements, per competitive philosophy, are usually banned from tournaments, or users of them at the very least frowned upon: if a broken technique is not dealt with, the concern is that the game would simply degenerate into both players trying to be the first to make use of the broken element, as no other element would prove effective. Many casual players instead believe all parts of the games should be allowed; however, due to many broken elements being extremely frustrating to play against, there is a general consensus that using them excessively, or at all, ruins the fun.
Types of broken elements
Generally, broken elements in the Super Smash Bros. series come in two forms:
A third form of brokenness can exist: a character by itself, without the aid of stages or techniques, overpowers the rest of the cast to the point where no other character is viable in competitive play. Whether a broken character exists in the Smash series is heavily debated, though a few characters spark more discussion than others:
Though other characters have been at some points considered broken, none have been considered broken enough to be banned from most tournaments. In Brawl, the Ice Climbers were considered broken by many players, but a widespread ban was never enacted during Brawl's competitive life; following the release of Smash 4, they have been occasionally banned at the few Brawl tournaments hosted, such as Glitch 2.
The term "broken" is often used when describing techniques, characters, attacks, etc. in many competitive games. Many players are quick to label strong techniques as "broken" when they mean overpowered, or even just powerful. Though many accept this usage, it is often discouraged because it makes the usage ambiguous. There are alternate terms that are less ambiguous for these more emphatic sentiments, such as OP, stupid, or insane, while there aren't clear-cut synonyms for the other definition of broken.
More colloquially, broken can refer to elements that are buggy, or don't work as intended in all circumstances. Broken can also refer to game glitches that cause the game to become unplayable on a greater than superficial level, such as game crash or game data corrupting glitch.