[South Africa] A cup of tea with milk and one teaspoon of sugar, where the milk is poured into the cup before the tea. Variations are ISO 0, with no sugar; ISO 2, with two spoons of sugar; and so on.
This may derive from the “NATO standard” cup of coffee and tea (milk and two sugars), military slang going back to the late 1950s and parodying NATO's relentless bureaucratic drive to standardize parts across European and U.S. militaries.
Like many ISO standards, this one has a faintly alien ring in North America, where hackers generally shun the decadent British practice of adulterating perfectly good tea with dairy products and prefer instead to add a wedge of lemon, if anything. If one were feeling extremely silly, one might hypothesize an analogous ANSI standard cup of tea and wind up with a political situation distressingly similar to several that arise in much more serious technical contexts. (Milk and lemon don't mix very well.)
[2000 update: There is now, in fact, an ISO standard 3103: ‘Method for preparation of a liquor of tea for use in sensory tests.’, alleged to be equivalent to British Standard BS6008: How to make a standard cup of tea. —ESR]