Teh is an internet slang neologism most frequently used as an English article, based on a common misspelling of the. A common typographical error, this typo became a part of Internet slang and subsequently developed grammatical usages distinct from the.
It is not common in spoken or written English outside technical or leetspeak circles, but when spoken, it is pronounced te.
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Apparently:
Along with pwn, teh is a standard feature of leetspeak Originating from the common typo, it has become conventionalised in a variety of contexts. It is often used ironically, and can be used to mock someone's lack of techie knowledge or skills, as an insult, or to reinforce a group's elitism.
Furthermore, teh can be used in front of a verb in a novel form of gerund, and it has the ability to turn nearly any word into an intensified noun, which can take the place of a superlative. The best-known example of this is the word suck. Thus, the phrase "this sucks" can be converted into "this is teh suck" ("teh suck" being equivalent to the superlative "the suckiest"); the word pwn can be similarly converted (teh pwn or teh pwnage). The latter phrase is primarily used by the computer gaming community, and often intended humorously.
Crikey. It's amazing how wikipedia can take over teh world, and suddenly make typos into real words. Who wants to see it in the English dictionary? Geeks stand and be counted!