How would you define "valid"?"KJVO" stands for "King James Version Only". And a KJVO is a person who believes, or at least pushes the doctrine, that the KJV is the only valid English Bible translation out there, and that no other version is valid.
This is different from "King James Version PREFERRED", people who believe the KJV is the best version out there, but not the only valid one.
The KJVO doctrine, is, of course, false, & is only a man-made myth with NO Scriptural support.