A (marriage) proposal — the act of asking someone to marry you. Often used with 'suru' as 'to propose'.
彼はレストランで彼女にプロポーズした。
He proposed to her at the restaurant.
結婚のプロポーズを受けて、彼女は思わず泣いた。
She burst into tears when she received the marriage proposal.
プロポーズの言葉を一生懸命考えている。
I'm thinking hard about what to say for the proposal.