Fans of the Star Trek 'universe' have some shorthand acronyms when referring to the different series, characters, episodes, etc.

TOS - The Original Series
TNG - The Next Generation (the second television series, started 1987)
DS9 - Deep Space Nine - the spinoff series from TNG

Scotty's kilt wearing was discussed on XMTS in this thread. In summary, he rarely wore it, he had a fly plaid, and it was in the Scott Black and White tartan.

To continue with the Scotty quotes:
From TOS episode ‘By Any Other Name’
Scotty: [Trying to drink Tomar - a Kelvan crew member attempting to take over the Enterprise - under the table, Scotty enters, a bit tipsy, with a bottle of green liquid] I found this in the ganner room... ganner...
Tomar: What is it?
Scotty: It's, [looks for a label]
Scotty: uh, [looks under the bottle; sniffs it]
Scotty: ... It's green.