In popular usage, an heirloom is something, perhaps an antique or some kind of jewelry, that has been passed down for generations through family members.

The term originated with the historical principle of an heirloom in English law, a chattel which by immemorial usage was regarded as annexed by inheritance to a family estate. Loom originally meant a tool. Such genuine heirlooms were almost unknown by the beginning of the twentieth century. (source)