Check In/Check Out a document
Check In/Check Out feature in Zoho Docs helps the team in managing documents effectively in a collaborative environment. It allows only one person to work on a shared document at a time, and prevents other shared members from overwriting each other's updates.
Check-Out : Checking out a file means you have exclusively locked the file for editing for yourself. This allows you to work on the file without having to worry about other people modifying it. It will also show which team member has checked out the file for editing. That way, everybody knows who is currently working on it.
Check-In : Checking in a file means you are uploading the modified version of the file to the document management system. Once the check in is completed, the said file is available for other shared users. You can leave a comment describing the changes that you made to the file, when you are checking it in. Consequently, other shared users can see the history of changes made to the document.
for more:
http://www.zoho.com/online-document-management/checkin-checkout.html