Dutch acronym for the phrase "tot en met", which means "up to and including".
"Up to and including" is a concept that the English language doesn't seem to have embraced quite as fully as Dutch has. For example, when a tourist attraction says it is open from "April to October", does it mean from April up to and including October, or does the period only stretch to the end of September?
The phrase "up to and including", while allowing for greater accuracy in expression, sounds clunky, and is thus rarely heard. Hence, the very concept is only used in specific circumstances (e.g. set theory). In Dutch, "tot en met" is a sharp snap of a phrase, and is used regularly and to good effect.
Yet another example of how other languages can also imply a completely different way of thinking about the world.