other people's money
Refers to money belonging to someone else, often with a nuance of not being one's own to spend freely.
人の金で贅沢をするのは簡単だ。
It's easy to be extravagant with other people's money.
Compound of 人 (hito, 'person') + の (no, possessive particle) + 金 (kane, 'money').