Refers to a person who borrows something, typically money or an item. Not a highly common word; 借り手 (かりて) is more frequent.
The bank presented a repayment plan to the borrower.
At this library, a borrower can check out up to five books at a time.
Compound of 借 (かり, 'borrowing') and 人 (にん, 'person'). The reading かりにん follows standard on'yomi patterns for such compounds.