pop-up hint; tooltip; mouse-over explanation
A small explanatory box that appears when hovering over an element in a user interface. Wasei-eigo from English 'pop hint'.
wasei-eigo (Japanese-coined English), from pop hint
When you place the mouse over the icon, a pop-up hint appears.
このボタンのポップヒントには「保存」と書いてある。
The tooltip for this button says 'Save'.
Variant with a middle dot; less common but still seen.
Wasei-eigo from English 'pop' (as in pop-up) and 'hint'. Not a direct borrowing from English; the English equivalent is 'tooltip' or 'pop-up hint'.