"Default browser" refers to the internet browser that is automatically opened when you click on a web link or access the internet. It is the browser that your device uses as a primary option unless you choose to use a different one. Full definition
There is a current default browser and you are asked if you would like to make the new browser your default. (voicebot.ai)
This would allow enterprises to manage these settings in one place, simplify migration to IE11 and allow adoption of Edge as default browser in IE10 (blogs.windows.com)
Apart from the preloaded apps, the Alcatel OneTouch Fierce XL will also pack features such as Cortana, Microsoft's digital voice assistant, and Microsoft Edge, the new default browser for Windows 10. (gadgets.ndtv.com)