Warming food in the microwave with レンチンする
レンチンする means to heat food in a microwave. It abbreviates レンジでチンする: レンジ refers to a microwave oven, and チン imitates the bell on older models.
Examples
Heating leftover pancakes with チンする

During Jumbo’s visit, Yotsuba tells him she made pancakes earlier.
- よつば:
- 「まだちょっとのこってる!チンしてたべるか!?」
- “There's some left over! Shall I heat it up to up to eat?”
- ジャンボ:
- 「おう。よつばが作ったんなら食
( べなきゃな」- “Sure. If you made them, I have to eat some.”
Lunch is heating with レンチンする

Satsuki is left to watch Sara for the day. As the afternoon arrives, Satsuki discovers their lunch had already been prepared and placed the refrigerator, with a note saying to heat it and eat it.
- 皐
( : - 「今
( レンチンしてるから待( ってね〜」- “The food's heating up right now, so wait a bit, okay?”
- サラ:
- 「わーい!」
- “Yay!”