What Does Default Browser Mean?
Default browser refers to the browser that is associated with Web documents or Web links. It is also the browser that comes pre-installed with the operating system, e.g., Internet Explorer for Windows, Safari for Apple's Mac OS or iOS.
Techopedia Explains Default Browser
The default browser is the application that is automatically launched when a user clicks on a Web document or when an application opens a Web link, such as when going to its home page.
There are several browsers available for users to choose from, each of which can be installed side by side with other browsers. However, only one browser can be associated with a Web document. The user must explicitly choose a different browser if he/she wishes to open the document with a different browser or, alternatively, he/she should change the file association.