noun
heavy spending on virtual goods; whaling
Used in gaming and social media contexts for users who spend large amounts of real money on in-game items, gacha, or premium features. Often carries a slightly critical or self-deprecating tone.
彼はソーシャルゲームに重課金している。
He spends heavily on social games.
重課金勢と呼ばれるユーザーが売上の大部分を支えている。
Users called 'whales' support most of the revenue.
微課金 means 'light spending' or 'small purchases', the opposite of 重課金.
Compound of 重 (heavy) and 課金 (billing/charging), literally 'heavy billing'. A relatively recent term from online gaming and social media culture.