For folks who evidently disagree with this, consider that DSL has another common tech meaning. More common, for quite a lot of people, who may even be programmers. Defining initialisms and abbreviations upon first use used to be a basic assumption in most writing, and in most teaching of writing. It’s probably fine to assume some knowledge based on your expected audience, but when your audience tells you it doesn’t have the knowledge you assume, it’s okay and even good to have a little humility about your mistaken assumption.

In this case it means "Domain-specific language". SQL is a great example of a DSL. https://en.wikipedia.org/wiki/Domain-specific_language

I’m presuming Domain Specific Language, as the context refers to a “target domain.”

https://en.wikipedia.org/wiki/Domain-specific_language