雷 (léi) is a noun meaning "thunder." It refers to the loud sound produced during a thunderstorm. In modern slang, 雷 can also mean "shocking" or "mind-blowing," but its primary meaning remains the natural phenomenon of thunder.
外面雷声很大,把孩子都吓哭了。
Wàimiàn léishēng hěn dà, bǎ háizi dōu xià kū le.
The thunder outside was so loud that it scared the children to tears.
远处传来一阵阵雷的声音,暴风雨快来了。
Yuǎnchù chuán lái yī zhènzhèn léi de shēngyīn, bàofēngyǔ kuài lái le.
Rumbles of thunder came from the distance — a storm is coming soon.
夏天的雷总是来得又快又猛。
Xiàtiān de léi zǒngshì lái de yòu kuài yòu měng.
Summer thunder always comes fast and fierce.