The phrase "default printer" refers to the printer that is automatically chosen by a computer or device as the primary printer to send documents or files to, unless you specify a different printer. Full definition
Printer, paper and print: Set up several default printers in multiple locations. (thewindowsclub.com)
Still, it could always be easier and this is why Android Oreo «s default printer service is using technology that was contributed to AOSP by Mopria. (xda-developers.com)
You can manage this behavior in Settings > Devices > Printer & Scanners to change this to the previous way Windows handled default printers. (blogs.windows.com)