Lambda the Ultimate

What is the relationship between a "language" and a "domain" in the term DSL? I suspect we curently apply just a subjective ontology: some languages are intended to cover a specific domain and are therefore domain specific. But aren't Erlang, C and Perl also domain specific in this respect ( telecommunication networks, operating systems and text processors )? We are just widening and narrowing abstractions and also domains and unless we don't simply focus on surface syntax ( what almost any author inevitably does who is talking about DSLs ) it's pretty hard to designate a domain specific language. For instance we could replace this ugly line noise that regular expressions are by a combinator library without changing the underlying semantics. Do we have a language only in the first case but not the last?