noun
Refers to the act of buying or the thing bought. Often used in compounds like 買い物 or 買い手.
今日は買いに行く時間がない。
I don't have time to go shopping today.
これはいい買いだった。
This was a good purchase.
noun
Used for a person who buys, especially in contrast with 売り (seller). Common in set phrases like 買いが少ない.
今日の市場は買いが少ない。
There are few buyers in the market today.