A textual critic is often faced with a dilemma: the variants in all the surviving witnesses are for some reason unsatisfactory, and he or she is forced to make an educated guess about the proper reading of the text. When a textual critic proposes a reading that doesn’t appear in any of the witnesses, it’s called a conjectural emendation.
Note: This guide is still in the early stages of development.
Three question marks mean I have to write more on the subject. Bear with me.