Tank can refer to:

• An artificial body of water, or a man-made reservoir, especially in India where the word originated, and sometimes in Britain.
• A large container for liquid, hence also an aquarium, or terrarium (derived from the above meaning).
• An old name for swimming pool, from which the upper portion of a bathing costume, the tank top, is named.
• A container for a compressed fluid, especially a gas cylinder.
• Tank, a type of armoured combat vehicle.
• Tank, Pakistan, a small town in Pakistan's North-Western Frontier Province .
• Informally, to tank means to decline dramatically, as in a stock declining rapidly in price, or a film failing in the box office.
• The fictional character Tank from the film, The Matrix.
• A warrior or similar character in a computer role-playing game that acts as a meat shield for other characters.

The word may have some connection with the Arabic verb istanqa`a, "it [i.e. some liquid] collected and became stagnant".