Pretty sure most of you already know this but for those who don't: you have two clipboards in Linux. One is the traditional clipboard where you copy with control c and paste with control v. The other one is when you highlight text and use the mouse middle click to paste text.
More details here.
Ironically neither GNU nor Linux has a clipboard (well GNU Emacs probably has like 37 of them for some reason). "Primary selection" (the other clipboard that people don't tell you about) started off on X11, which of course had to implement by XFree86, which became Xorg, and then it copied (ha ha) by other non-X-related software like gpm and toolkits like GTK when using Wayland.
Emacs's regular clipboard is the "kill ring" which also allows you to retrieve any previously cut/copied text. It also has "registers" where you can store and retrieve snippets of text, which can be considered clipboards when used for this purpose. Registers can be referenced by any character you can type on your keyboard, including control characters like ^D.
This totals… a lot of clipboards.