Ki, is a important matter. Ki, is a force of energy, which translates as ' Life Force ' in English. This force is a energy, inside every living being, its major focus being in the center of the body. By drawing it out, a person is able to manipulate it and use it for techniques outside the body. Ki can be used for many different techniques, usually more concentrated the masses are, the more time the user requires to draw it out ( Or Power Up ). When a person uses Ki, the person is able to gain enhances strength, speed, and durability, and can increase the power of their attacks to inflict greater damage to opponents.
Thats a rundown on Ki, not all races start with Ki, races that don't start with Ki say so in the list of ' Races ', and so they have too learn it.