1. proficiency and/or talent.
2. The outcome resulting from such proficiency or talent.
The term probably originated from boxing where close, tight punches are considered good form, whereas wild, open punches are poor form. If a fighter starts to swing wildly (throwing haymakers), his coach might yell out something like "Tighten up!" or "keep that shit tight!".
2. "Wow! Did you see that? That shit was TIGHT!"