The number representing no quantity; nothing.

• The integer between negative one and one, written 0.

The digit 0 in any numeral system.

• The value or reading at the starting point of a scale.
• A total amount of none.

A value where a function equals zero; a root.

Having no quantity; none.

• Of visibility or cloud ceiling: extremely low or none.
• In product names: containing no calories or sugar.

To set a value to zero.

• To calibrate an instrument so its reading is zero.
• To reduce error or offset to none.

A person regarded as unimportant or ineffective.