The law distinguishes between contracts which are void and those which are voidable.
Some contracts have such a latent defect, some vitiating element, that they are said to be void (see definition of void).
Other have more minor defects to them and are voidable at the option of the party victimized by the defect.
For example, contracts signed by a person when they are totally drunk are voidable by that person upon recovering sobriety.