The term 'legally invalid' refers to something that is not legally binding or recognized by the law. It is often used to describe a document, contract, or agreement that has been declared void or unenforceable by a court of law. This could be due to a variety of reasons, such as a lack of proper signatures, incorrect wording, or a violation of existing laws. In any case, the result is that the document or agreement is not legally valid and cannot be enforced.