1
three Cs;three conditions that facilitate the transmission of infectious diseases (closed spaces, crowds, and close contact)
in ref. to 密閉, 密集, 密接
2
three mysteries (Buddha's body, speech and mind)
usu. 三密
Other forms
三密 【さんみつ】 · 三蜜 【さんみつ】 (search-only kanji form) · ３蜜 【さんみつ】 (search-only kanji form)