TSR

n.（名詞）
A program, such as a spell checker or calendar, that remains loaded in memory so that it may be quickly recalled while another program is running, as found in operating systems which do not allow multitasking.
常駐程序：一直存在于內存中的程序，如拼字檢查或月歷，在不允許處理多任務的操作系統(tǒng)中其它程序運行時其可被即刻恢復

來源：
t(erminate and) s(tay) r(esident)
t(erminate and) s(tay) r(esident)