Definition:
It is a process of improving quality and productivity by preventing the injection of defects into a software product. There are following parts to manage the process:
Defect Prevention, Baseline delivery, Defect Discovery, Defect Resolution and Process Improvement.
Defect Prevention is much more efficient and effective in reducing the number of defects and also is very cost effective to fix the defects found during the early stage of the software process. Most of the organizations conduct Defect Discovery, Defect Removal and then Process Improvement which is collectively known as a Defect Management Process.
Further Reading:
Book: Disciplined Agile Delivery by Scott W. Ambler and Mark Lines.