"Onboard graphics" refers to the graphics processing unit (GPU) that is built into the motherboard of a computer. It is responsible for displaying images and videos on your computer screen. Full definition
It's important to note before we start though, that some of these games are not designed to be run using onboard graphics. (digitaltrends.com)
Laptop manufacturers have a choice — they can include onboard graphics for better battery life or discrete graphics hardware for better gaming performance. (howtogeek.com)
On some laptops, you may also be able to enter the BIOS or UEFI firmware settings screen and disable your discrete GPU to force Linux to use only onboard graphics without any additional tweaks. (howtogeek.com)