A "quiet zone" is placed around the QR code image when it's generated to separates the QR code from anything else in its surroundings. The quiet zone is used to buffer the code from its surroundings to prevent any adjacent images or text from being interpreted as part of the code image itself and interfering with the scanning of the code.
The size of the buffer zone is mathematically determined when the code is created to ensures an error free code. This buffer zone must be retained. It's simply a white space border and when you generate the code you will see that it's part of the actual code image.
The quiet zone is recommended to be a minimum of 4 times the width of a single data square in the code image, however depending on the surroundings of the code (ie; against an unpatterned dark background) you may be able to reduce that to 2 times pixel width.
If you reduce the size of the quiet zone, the finished QR code should be tested thoroughly in its intended final setting to make sure that it still scans correctly.