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screen Terminology
session A screen session is a single collection of windows all running with the same grouping. Copy and paste only work within a particular session, and all window numbers within each session are unique. There is a single master screen process for each session.
window A session can contain multiple windows. Each window can run a different program (by default, windows are created running a shell). Each window has a number unique within that session. It also has a name, which does not have to be unique.
display This refers to where the screen session is attached; if being specific, it refers to the terminal or pseudoterminal used by the attaching process. See pseudoterminals and screen.