Obstructed View, Limited View, and Partial Obstruction are all terms used to indicate that attendees in certain seats may not have a full view of the entire performance.  Every venue and obstruction is different, and not always the same from event to event.  The venue decides if a particular view is partially blocked and are responsible for printing the disclaimer on the tickets.  All sellers are required to include these disclaimers when listing their tickets for sale, but may not know the specifics of what or how large the obstruction is.