Some of the most common terms and abbreviations you may find on my blog:
Polyamory- The practice of dating more than one person at a time. Not just sleeping with multiple partners, it is the belief that it is possible to have multiple committed relationships.
Poly- Short for polyamory as well as polyamorous. People in polyamorous relationships will often refer to themselves simply as "poly."
OSO (Other Significant Other)- Your partner's other partner. If I am dating Jack and he is dating Jill, Jill is his OSO
Triad- Three people in a relationship, all dating each other. A dates B, B dates C, and C also dates A
Primary Partner- For me, this is a person I am creating a strong relationship with, not just someone I'm dating "for fun"
Secondary Partner- Conversely, this is the person I'm dating "just for fun"- not trying to see a long-term future.
DADT (Don't Ask, Don't Tell)- The practice in some poly relationships of preferring to live in ignorance.