From Gentoo Wiki
Hi am a n00b to Gentoo, but I made an account here because this first page threw me off when I was preparing to install Gentoo. It constantly uses rather specific wording to say to burn the ISO to a CD. I knew there was no logical reason why a CD should be necessary over a USB stick, but the fact that the official handbook used such specific wording made me wonder if there might be some reason. As Gentoo has a notoriously steep learning curve, this wording caused me to delay even trying Gentoo. Trying Gentoo is enough of an experiment, I didn't want to try it the first time and go against the very clear wording of the guide.