Zero is the basis of a small set of terms and idiomatic phrases, which are listed and defined below.
Zero derives, through French and Italian, from the Latin term zephirum, which in turn stems, as do the other mathematical terms algebra and algorithm, from Arabic: Sifr means “cipher” (and is the origin of that word as well). Sifr, in turn, comes from Sanskrit.
Absolute zero (quantified as 273.15 degrees below zero Celsius) is the temperature at which matter stops moving, while ground zero is the origin point of a phenomenon. (Originally, it referred to the blast site of a thermonuclear explosion.) Zero hour is the time at which something is scheduled to begin.
Zero gravity and zero visibility refer to a near, not absolute, absence of the qualities referred to in the phrases, and patient zero is the first person to contract a disease in an outbreak.
The colloquial expression “From zero to hero” denotes a change in state from anonymity or a lack of distinction or popularity to fame, from the sense of zero as meaning “an undistinguished or worthless person.” (One can also, unfortunately, transition in the other direction as well.)
To zero in is to focus on something or to come closer to it; the expression stems from the idea of adjusting a setting on a device or instrument to zero but originally applied to shooting a firearm. To zero out is unrelated—it means either to reset something, such as timer, or to cut off funding or reduce a quantity.
Zero tolerance is the concept of absolute adherence to a rule; the phrase has entered mainstream discourse in references to zero tolerance for weapons or illegal drugs in a given area or jurisdiction. A zero-sum game, meanwhile, is a situation in which a defeated competitor or participant loses as much as the victor wins. (The sum of the gains and losses is zero, hence the name.)