It refers to that no drugs (though not as much towards alcohol since the alcohol companies help fund anti-drug organizations bullshit) are acceptable to be taken recreationaly. Pure abstinence over drugs. Too bad for them humans don't work that way. There have been drug users for as long as humans have known of their existence.
And people looking to sell them will always exist no matter how draconian the laws are.
Zero tolerance once again = zero intelligence
To react to a proscribed activity or substance with absolute prejudice... Without regard to mitigating circumstances or conditions.
We will react to sexism and racism with zero tolerance.
In practice, zero tolerance policies allow for no weapons or dangerous objects in school.
However, the noun "weapon" can mean "an object that can be used to cause harm"; the phrase "dangerous objects" is a plural of the same meaning; therefore, almost any object can be considered a weapon.
Because of this, overzealous officials often unleash horrificaly exaggerated sentences for the silliest of things.
Zero Tolerance laws exist to punish the innocent. The guilty already are already fucked so having strict, uniform punishments regardless of the circimstances of the "crime," the persons criminal record and the persons intentions is just stupid.
Anybody who supports zero tolerance policys need to be thrown into a concentration camp until they arent dumbasses. For I have zero tolerance for stupidity.
As far as school zero tolerance policys go, read around www.zerointelligence.net.