“扫地” means “to sweep the floor,” and “僧” means “monk.” The sweeping monk who provided the origin for this term is a character from Jin Yong’s martial arts novel “天龙八部” (tiānlóng bābù, “Demi-Gods and Semi-Devils”). A low-ranking figure unknown to the world whose daily job is to sweep the floor in a tower where Buddhist scriptures are stored in Shaolin Temple, the sweeping monk later turns out to be a top martial arts master. Therefore, Chinese netizens use the term to refer to those who appear to be ordinary but are in fact the top elites in their industry or field.
Tīngshuō nǐmen xiǎoqū yǒu ge bǎo’ān huì shūfǎ？
I’ve heard that a security guard in your housing estate is good at calligraphy.
Shì a，guònián de shíhòu hěnduō línjū qǐng tā bāngmáng xiě chūnlián，wǒmen dōu méi kànchūlái，shēnbiān jìngrán cáng zhe yīgè sǎodìsēng。
Indeed! Many of my neighbors asked him to write their Spring Festival couplets. We didn’t know that he is an elite calligrapher in disguise.