A simple input/output device with no local processing power, used to connect to a mainframe or server. Technical computing term.
In old banks, they used dumb terminals to connect to the mainframe.
端末 is a general term for any terminal or device, while 簡易端末 specifically refers to a dumb terminal with minimal functionality.
シンクライアント (thin client) is a more modern term for a lightweight terminal that may have some local processing, whereas 簡易端末 is an older term for a completely dumb terminal.
Compound of 簡易 (simple, easy) and 端末 (terminal, device). A straightforward technical term with no obscure historical derivation.