When a document (file, meeting, task, discussion, policy) is being edited the item is 'Locked' so that other users cannot attempt to make changes at the same time. If users look at a document that is locked they will see the version before any changes are made.
You can see if a document is 'locked' as there will be a blue bar showing it is locked and who has it locked.
If the person editing the document does not either 'Submit' (save changes) or 'Cancel' (abort changes) then the document remains 'locked'. The decision to 'Lock' a document may be intentional to prevent other users from editing it.
Only the person who locked the item, or a GVO Manager can unlock a locked document by pressing 'Cancel'.