End-of-Life (EOL) means the date set up by the Original Equipment Manufacturing (OEM) to longer sell, support, update or upgrade or patch, extend warranty or cover your product such as an electronic device, operating system (OS), or an equipment.
Usually major companies such as Google, Apple, IBM, Microsoft, HP, Cisco etc. will announce the EOL for their products, but it may be hard to search, track, and find out that information.
endoflife.date is a useful website which documents EOL and support lifecycles for various products to help you track EOL dates for major devices and OS.