If I want to copy a password I click on the green box that says "Copy". Then I get a yellow message that says "Password copied to clipboard." That message quickly disappears. Where is the clipboard? What is the clipboard?
The clipboard is a generic computing term.
"The clipboard is a software facility used for short-term data storage and/or data transfer between documents or applications, via copy and paste operations."
You can refer to this article for further information.