Principle of Verification

"We say that a sentence is factually significant to any given person, if and only if, [she or] he knows how to verify the proposition which it purports to express—that is, if [she or] he knows what observations would lead [her or] him, under certain conditions, to accept the proposition as being true, or reject it as being false."

AJ Ayer - Language Truth and Logic 1936

In other words, something has "meaning" (whatever that is) if it can be tested to establish whether it is true or false.