valid
An argument is valid if its premises being true would guarantee its conclusion is true.
An argument is valid when it is impossible for all of its premises to be true while its conclusion is false. Equivalently: if the premises were true, the conclusion would have to be true; the conclusion follows from the premises. Validity is about the link between premises and conclusion, not about whether they are actually true.
Examples
"All fish can fly. A trout is a fish. So a trout can fly." Valid, though the first premise is false.
"All dogs are mammals. Rex is a mammal. So Rex is a dog." Not valid, though every claim may be true.
See also