Having no title.
"The artist presented a series of untitled sketches that invited viewers to project their own stories onto the blank canvas."
In plain English: Untitled means something that has no name given to it yet.
"The untitled manuscript sat on the desk, waiting for a name to be chosen."
The word untitled combines the prefix un- with titled to mean lacking a title. It entered English as a straightforward negation of the concept of having an official name or designation.