Don't confuse a deficiency of a wikipedia article for the definition of that thing.

So where should I look up the definition of a DSL?

Let's take the Wikipedia definition, not the examples list:

> A domain-specific language (DSL) is a computer language specialized to a particular application domain.

where computer language links to a list of things that includes "programming languages", which visual programming languages are a part of.

Other sections of the article also mention some graphical examples, e.g. UML. (which isn't a programming language, but a modeling language, also used sometimes as an input to software)