Usually it means they are extremely over powered. Like, in Mortal Kombat Trilogy, Noob Saibot moves faster then everyone else and his disabler comes out super fast and it holds them for a really long time, all leading to him being broken. MK2 Kung Lao in MKT is another example. It is so much easier to get damage with him then it is with most characters that he seems broken to many. His autocombos alone do tons of damage because he does all Mortal Kombat 2 level damage. Characters like Human Smoke and Ermac also do tons of damage, and they are very powerful but it's just not as easy with them, although I think ermac is still a little broken as well since he has soooo many 100% damage combos.