A Configuration Management System is a system which applies administrative control over the life cycle of a document or program. Such a system monitors its subjects, keeping track of proposed changes and their implementation; it is informed about the status of its subjects at all times. This system ensures that any proposed change does not affect the item's compliance to specifications, or its compatibility with any interface or contract requirement.
A Configuration Management System can be used to insure that upgraded software will still work with programs that it was able to work with in the past. CM can keep you from that nasty moment when you discover in mid-document that your upgraded word processor will no longer let you import files from your trusty spreadsheet program.