one's own money; personal funds
Refers to money that belongs to oneself, as opposed to someone else's money or company funds. Often used in contexts like paying from one's own pocket.
I paid the travel expenses out of my own pocket.
彼は身銭をはたいてその絵を買った。
He spent his own money to buy that painting.
Compound of 身 (oneself) and 銭 (money). The exact historical derivation is uncertain, but the meaning is transparent from the components.