[90s_dev]

Most people think of DSLs as a language you can create within a language. All the things you named are either entire languages themselves like HTML, SQL, and the shell family, or formal extensions of existing languages like JSX. A DSL would be something you could create inside JS tagged literals or Ruby.

[ChadNauseam]

I don't think of DSLs as strictly being embedded in another programming language. The term I would use for that is "eDSL", short for Embedded Domain Specific Language. See: https://wiki.haskell.org/Embedded_domain_specific_language

[fuzztester]

Martin Fowler on DSLs, including internal and external DSLs:

https://martinfowler.com/books/dsl.html

https://martinfowler.com/dsl.html

Also see:

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

including the References section.