A speedtalk is an oligosynthetic language with such a large phoneme inventory that the number of phonemes equals the number of morphemes, and all morphemes are just one segment long. The principle is to decrease the number of morphemes and to increase the number of phonemes until both meet in the middle. It is assumed that this yields the fastest language possible, though this remains to be tested.
The idea and the name "Speedtalk" are from the story Gulf (1949) by Robert A. Heinlein. In Gulf, Speedtalk is a logical language with a minimal vocabulary and a maximal phoneme inventory. In the story, however, the idea is merely outlined and no detailed description of the language is given.