1a flat board used for chopping or cutting food (chopping board/cutting board).
毎朝このまな板で野菜を切ります。
I cut vegetables on this cutting board every morning.
まな板を使った後はよく洗って乾かしてください。
After using the cutting board, wash it well and dry it.
木のまな板は包丁の刃にやさしい。
Wooden cutting boards are gentle on knife blades.
俎板に魚をのせて捌いた。
I placed the fish on the cutting board and filleted it.
2slang, vulgar term referring to a flat chest (very small breasts).
彼は冗談で彼女のことを「まな板だ」と言ってしまった。
He joked and called her "a cutting board" (flat-chested).
そんな言い方は失礼だ。人の胸のことをまな板なんて言わないで。
That way of speaking is rude. Don't call someone's chest "a cutting board."