Broken: in MK is a tool/move that breaks the meta and at the same time gives advantage to a single character over the entire cast. the problem with alot of people misusing this term is a character can be strong with many tools used together, none of them being broken at all, but at the core the fighter has it all and is able to handle any matchup like Mileena, she doesn't really have any move or tool that is truley broken but because of her data and toolset she has favorable matchups across the board.
Overpowered can be used to describe a character as whole or simply a move that is well Better than all other characters that use something similar. like aliens B3, perfect example would be its the only character that can almost full screen mix up. but what would make a character Broke would be aliens JIP2 which auto corrects, alien jip2's you and wiffs but still has advantage like alien hit you with it. that would be an example of how a move breaks both the meta and breaks game mecanics and at the same time allows alien to have an advantage over the cast, and alien does because has mixups like the rest but at farther range than the rest and can not be punished even if it was negative because of the range, but more so because of the Jip that noone else has.
Certain characters are given tools that other characters do not have to deal with certain situations.
like lets say i am kenshi, and my wakeup has limited option's and im against a Jax/ Alien, well i get knocked down OFC itll happen, and i try this time to Meter burn wakeup, well Jax has a 2 hit normal that breaks armor and at the end of it mixes up the opponent, so not only does that tool he has but i do not have break armor, and one of my only options this character has been given something i do not have, and its not fair for many matchups that don't have that tool to use.
Kenshi would have to use something like Xray to do something like that which cost him all 3 bars, while Jax only has to use a normal for zero bars and can do it freely.
BTW its an Example and im not calling Jax Broken or OP.
but you get the idea. just having that tool does not make them broken, and kenshi is not a character to compare to the top. he kinda does not have what the top tier has so not a good comparison. but a character like Mileena or Alien has plenty of tools to deal with everything, now if Mileena had a JIP that auto corrected like alien and maybe another strong tool that broke the meta she would be Broken. one tools he does have is really broken, and that is her normal Ball roll, the first couple frames has a hitbox, then after she starts rolling toward you she has no hitbox, what makes her diofferent than lets say Cassie and her invulnerable NUTpunch is Mileena along with that BS game breaking no hitbox roll, she has all the tools to be an A+-S tier character.
Perfect examples of Broken from this game would be: Pre patch Tanya and her constant pressur with a teleport that jailed into more pressure and could not be hit out of air, allowing Tanya to loop pressur, and the game was not intended to allow a player to deny other players a turn.
Same concept with Pre patch Quan chi Summoner, when he could jail into Multiple mixups that lead to high damage and could be looped over and over and was very hard to block even by professionals. thats game breaking