Technische Hochschule (acronym TH) is what an Institute of Technology (i.e. a university focusing on engineering sciences) used to be called in German-speaking countries, as well as in the Netherlands, before most of them changed their name to Technische Universität (German) or Technische Universiteit (Dutch) (acronym: TU) in the 1970s (in Germany) and in the 1980s (in the Netherlands).
This has to do with the fact that, in the Middle Ages, an educational institution was called a (medieval) university only if a certain classical canon of subjects was taught (including philosophy, medicine, law and theology).
In modern times, other subjects, namely engineering sciences became more important — but still, institutions of tertiary education focusing on these and not offering the classical canon were denied the prestigious denomination "university", so they had to use the general word Hochschule (higher school, i.e. school for tertiary education).
A major break-through was hence, when, in the first half of the 20th century, some Technische Hochschulen in Germany and Technische Hoghescholen in the Netherlands were given the right to award the doctor degree, and later, they were allowed to call themselves universities — in accordance with the usual distinction that defines a university as an institution of tertiary education that can grant doctorates.
Some THs, however, preferred to maintain their traditional and established names, most notably the RWTH Aachen and the two THs in Switzerland (ETH Zurich and EPF Lausanne). Universities that changed their names from TH to TU include TU Delft and TU Eindhoven in the Netherlands.