Master may refer to any of the following:
1. In Git, the master is the name for the main branch. For example, when you clone a Git project to your computer, you create a master of that project on your local repository known as the master branch. From the master branch, you can create new branches with new features or fixes and merge those into the master branch or make changes directly to the master branch.
2. A setting adjusted using a jumper found on a computer peripheral, such as a hard drive, as shown below. This setting sets the drive to be the primary drive and allows for multiple devices to connect to a single connection. Computers can only have one master per channel on a single IDE/EIDE cable and other drives connected to the same cable would be set as secondary or cable select.
Because "master" in this context is offensive, it's better to refer to this drive as "primary" or "device0."