hand-me-down; used article (esp. clothes)
Polite prefix お + 古 (old). Refers to used items passed down, typically clothing, but can extend to other goods. Common in family contexts.
I got my older sister's hand-me-down clothes.
このおもちゃは従兄弟のお古です。
This toy is a hand-me-down from my cousin.
お古 is the everyday polite word for a hand-me-down or used item, while 古 alone is a bound noun/prefix rarely used by itself in this sense.
Polite prefix お + 古 (old). The reading ふる is a native Japanese word for 'old' or 'used'.