"Valid" is used by logicians to describe an argument or syllogism in which no logical fallacies are made. This is not necessarily Sound logic, because the premises may be false. For instance, the following syllogism is valid but has a false conclusion:
All animals are dogs. (False premise/All A are B.) All dogs are terriers. (False premise/All B are C.) Thereforse, all animals are terriers. (False conclusion: not all animals are terriers. Valid logic: If all A are B, and all B are C, then all A are C.)