Japanese onomatopoeia for a bell ringing, with two tones. The original noise was borrowed from game shows where whenever a correct answer was given, the tones would ring out.

It is now also included in casual conversations where there is one person trying to teach and be cute at the same time. It helps lighten the mood.

For an idea of what it sounds like in actual speech, try imitating the prototypical doorbell noise, "ding dong!"