Conversation so far:
is slang specific to a particular group
Slang can be either culture-wide or known only within a certain group or subculture.
when was the term slang first used
In its earliest attested use (1756), the word slang referred to the vocabulary of low or disreputable people.
did anything change about the term slang or how it was used in the nineteenth century
By the early nineteenth century, it was no longer exclusively associated with disreputable people, but continued to be applied to usages below the level of standard educated speech.

Question: where did the term originate
Self-contained rewrite: where did the term slang originate