What are Helvetisms?
Helvetia is the Latin name for Switzerland. You can find this name on Swiss Franc coins and stamps. This is why the internet country domain of Switzerland is .ch (Confoederatio Helvetica).
Helvetisms are features distinctive of the German spoken in Switzerland, called Swiss Standard German. They distinguish it from the German spoken in Germany. The most frequent Helvetisms are in vocabulary and pronunciation, but there are also some distinctive features within syntax and orthography.
Swiss Standard German (GER: Schweizer Standarddeutsch), or Swiss High German is referred to by the Swiss as Schriftdeutsch (Written German), or Hochdeutsch (High German, i.e., the German spoken in Germany). The German-speaking Swiss (65% of the country’s population) learn to read and write in Swiss Standard German.
Remember: Swiss Standard German does not refer to the Swiss German Dialect (GER: Schweizerdeutsch, Dialect: Schwiizertüütsch), but to a variety of the Standard German spoken in Germany, i.e., the one taught at schools or institutes like the Goethe-Institut worldwide.
Most Helvetisms are NOT dialectal
The definitive work for German orthography, the Duden, explicitly declares a number of helvetisms as correct Standard German – albeit with the [schweiz.] annotation, denoting that the usage of the word is limited to Switzerland. However, not all words may be considered part of the “Swiss standard language”/”Swiss standard German” category, because frequency of usage must be evaluated as well; if this does not apply, or if a word’s use is known to span only one or more specific dialectal regions, the word must be categorized “dialectal” (German: mundartlich, often abbreviated mdal.).
Sources: https://en.wikipedia.org/wiki/Helvetism, https://en.wikipedia.org/wiki/Switzerland#Languages