I want to expand Takkats answer, since there are two different kinds of German spoken in Switzerland, and neither the question, nor Takkats answer addresses this difference:
Swiss Standard German
In German: »Schweizerisches Deutsch« or »Schweizer Hochdeutsch«
This is one of the three standard variations of German. It is a standard language, which means, that it is taught in schools, and it is used in official documents. There is a set of clear rules that defines whether a word or a sentence in correct Swiss Standard German or not. (For example: »parkieren« is correct, but »groß« is not)
In Standard German: »Schweizerdeutsch«
In Swiss German: »Schwizerdütsch«, »Schwyzerdütsch«, »Schwiizertüütsch«, (and much more different writings)
This is a group of Alemannic German dialects spoken in Switzerland. It is not a standard variation of any language. This means: It is not taught in schools, and it is not used in official documents. And there is not a well-defined set of rules which you could use to decide if a word or sentence is wrong or right.
And: It is not one dialect, but a group of many different dialects.
But Swiss German (the group of dialects) and Swiss Standard German (the standard variation of German) are so different, that it is hard to understand the other language, if you know just one of them.
And also very important:
Swiss German is used only to talk, not to write.
Swiss Standard German is used only to write, not to talk.
Well, this is simplified, because when for example something official has to be said by a politician, then he/she might use Swiss Standard German for talking too, and also some teachers talk Swiss Standard German when teaching students. And swiss people write Swiss German in internet boards.
Which is on-topic?
Both are on-topic.
- German Stack Exchange is dealing with modern Standard German in all of its three variations.
- German Stack Exchange is dealing with old forms of German (i.e. Old High German and others).
- German Stack Exchange is dealing with any German dialect.
(1) includes Swiss Standard German, and (3) includes Swiss German.