A tooltip is the little box of words that pops up when you rest your mouse pointer on something on a screen and wait a moment without clicking. It tells you what that thing is or does — hover over a small picture of a printer and a box appears saying 'Print'. It comes on its own after a short pause, and it goes away as soon as you move off; you never click a tooltip, and that is the point of it. Tooltips exist because designers use tiny pictures instead of words to save space, and pictures are not always clear. The tooltip is the quiet explanation waiting underneath. Two things follow from that. First, a good tooltip is short — a few words, not a paragraph. Second, tooltips are a real problem on phones and tablets, because there is no mouse and so nothing to hover with; designers have to find another way there, such as a long press. The word is used by ordinary computer users but belongs most to people who build software; a designer will say 'add a tooltip to that button' the way a builder names a part. You will see it written tooltip, tool tip, or ToolTip — Microsoft's original spelling — but one word is now normal.

工具提示、提示框（滑鼠移上去跳出的小說明）