ows_ is the SharePoint out of the box field prefix. It has been around since the start of time pretty much, and even though it is used for SharePoint Team Services it has kept the OWS name (Office Web Server) and why such things as search still comes from office.
[update - I know the answer was accepted but I thought I would put some history in here I dug it up for this post]
It was first SharePoint Portal Server before Team Foundation Server but the project was Codenamed Office Server which is where it all stems from.
Names of SharePoint:
Office Server (This came from FrontPage and Team Pages)
Tahoe (This was Exchange, Dashboard, Portal, Search and Document management)
SharePoint Portal Server
SharePoint Team Services
Windows SharePoint Services 2.0
Windows SharePoint Services 3.0
Microsoft SharePoint Foundation 2010
And that is how we still have ows floating around. Why we still have access through FrontPage RPC and why Office Portal controls the searching functionality.