Mine can mean several different things:

1. Something that belongs to you. When you say “that book is mine,” you're claiming ownership of it. If your sister tries to take your favorite pencil, you might say “Mine!” to remind her it belongs to you. The word is a possessive pronoun, related to “my” but used when the noun comes earlier in the sentence or conversation.
2. A deep hole or network of tunnels dug into the earth to extract valuable materials like coal, gold, diamonds, or iron ore. Miners work underground in mines, using tools and machines to remove these resources from rock. The California Gold Rush of 1849 drew thousands of people hoping to strike it rich in gold mines. Modern mines can stretch miles underground and use sophisticated equipment, though mining remains dangerous work. The verb form means to dig for these materials: workers mine for copper or mine coal.
3. An explosive device buried in the ground or floating in water, designed to detonate when disturbed. Naval mines threatened ships during wartime, while land mines posed dangers to soldiers and civilians alike. Because of their terrible effects, many countries have banned their use.
4. To search through something carefully for valuable information, like when researchers mine historical documents for clues about the past, or when you mine your memory trying to remember where you left your backpack.