A false premise is an incorrect proposition that forms the basis of an argument or syllogism.
However, the logical validity of an argument is a function of its internal consistency, not the truth value of its premises.
For example, consider this syllogism, which involves a false premise: This argument is logically valid, but quite demonstrably wrong, because its first premise is false — a street cleaner may have passed, the local river could have flooded, etc.
Another feature of an argument based on false premises that can bedevil critics, is that its conclusion can in fact be true.
Large language models often fail to appropriately answer questions based on false premises, but can be trained to respond correctly.