Triazepan for what it is for

What does “hoch” stand for in the term “Hochdeutsch”?

The term "Standard German" has two meanings:

High German as a contrast to Low German

Low German is the colloquial language (i.e. the German spoken in everyday life) in the more northern areas of the German-speaking area. High German describes what is spoken in the south. The border is the approximate line Düsseldorf-Kassel-Leipzig-Cottbus. (Google and Wikipedia know details.)

The syllable "high" comes from the geographical location. High German is spoken in higher elevations and Low German in the plains.

Standard German as a contrast to dialects

At no time, neither in the past nor in the present, was there / is there a uniform German. German has always consisted of a multitude of different dialects, and there have been many attempts over the centuries to standardize these dialects.

Standard German is the current attempt to create a uniform standard for the German language. High German is to be understood as upscale German. A synonym for this is "Standard German".

In Germany in particular (and in non-German-speaking countries), word has not yet spread that there are three different variants of standardized High German, because Switzerland, Austria and Germany have three very similar, but not exactly the same, standardizations of the German language that are also used by the local press. The differences between these three standards provide material for entire shelves of specialist literature.