Super armor is a defensive mechanic that allows the character to take damage without being flinched (i.e. does not stagger or recoil while being hit) and cannot be knocked out and is a step below invulnerability.
It is named after the super armor effect in the console game. However, in the mobile game, it is not a normal, named game mechanic, but mostly an unannounced side-effect.
Super armor is mostly seen at the beginning and end of Special Attacks, as a slight extension of the near-invulnerability offered during most of the special. Some specials have particularly long finishing animations and their super armor periods are more noticeable, such as at the end of Zod's s1, as well as Nightwing/Prime and Superman/Regime's s2s.