Transhumanist socialismTranSocialist Alliance definition)
Transhumanist socialism is a particular type of socialism which holds that future transhumanist technologies such as nanotechnology will make it much more feasible to bring about a truly socialist world.
A transhumanist socialist believes that despite the risks that may be involved in these new technologies, such as even more potent weapons and means of totalitarian control, it is on balance worth developing transhuman technologies in the long term, because of their potential to transform society for the better. (Note that this in no way necessarily implies that technology alone can solve problems. Everybody must change as well, because true socialism is not just a matter of who is "in charge", it is a mode of being of a whole society, on a world scale and including every person.)
Thus being a transhumanist and being a socialist are both necessary but not sufficient conditions for being a transhumanist socialist. It is at least logically possible to be a socialist and a transhumanist without accepting the further idea that transhuman technologies will be of significant benefit in their efforts to create a more just world - or one may be a socialist and believe that future technology can alleviate some important problems with "the human condition", but it still doesn't make world socialism significantly more feasible than it already is. Neither of these positions fall within transhumanist socialism - they are merely transhumanist and socialist, which is quite different.
Of course, the word "socialism" can mean many things to many people. Its usage here needs to be clarified.