What is writer's block?

For some time now, I haven't been able to write on the many manuscripts I have covering most of my laptop screen. I have made notes here and there, did some editing, made a few changes but those are a few items taking up only twenty minutes of my time. To finish a manuscript I need a full day's work. So in a way I have what many writers fear. Writer's block.  It may last for a few weeks, or years depending on the person or the case. Its been a few weeks so far for me. I have taken the time to read many books, keeping my mind sharp, and any ideas I have I still jot them down for a later use. It may take some time to finish the works I have, but as long as I do a little everyday, eventually they will be completed and who knows, maybe the wall that is preventing me from writing will come crumbling down and the words will flow from me again like a massive water fall.