It can mean several things (need the full context to determine what the author meant), but most likely it means the length of the project.
This is not a PMBOK term and not a project management term in any reference. Project managers are (in)famous for creating their own lexicon that may or may not mean something to the rest of the world (including other project managers). I personally don't think high of project managers creating their own jargon just to impress others...