“Teh” is a common typographical error of the word “the” which has become adopted as an intentional mis-spelling, sometimes as lolspeak. This has occurred as long as there have been QWERTY keyboards and typewriters.
When “teh” precludes an adjective, it implies that the word is the ultimate specimen of whatever the quality is. For example, “teh suck” means “This sucks bad.”
Wiktionary mentions a similarity in usage to the Spanish word El. Teh can be used in grammatically different ways than the word “the”, in a similar way to the Spanish word el. For example, “teh” can be applied to adjectives, whereas “the” cannot; “He is teh stupid.” is an acceptable sentence, whereas “He is the stupid.” is not.
UrbanDictionary contains a total of 63 entries for teh.