Paralysis is a basic negative status which renders a player or mob incapable of casting skills (except skills designed to work in these conditions) for a short moment. In technical terms, Paralysis forces the target into a "flinching" animation for a short moment, allowing the attacker to use skills with impunity. This status is inflicted when enemies super armor is broken and they don't get knocked back, knocked down or lifted, and the duration of paralysis can be increased by equipping items that add Paralyze stat. On the other hand, decreasing the duration of paralysis when being attacked requires equipping items that give Vitality or Paralyze Resist.
Take note that the effect of Restraint suffix has a different effect to that of Paralysis.