It's the number of posts you've made. I became a senior member in about a week, I think, because I posted several times to a couple of threads.. I think the magic number is either 15 or 20. I am a member of another board that uses the same software, and since I don't post very often, I'm still a junior member, despite being a member since November or December.I wondered about that at first too! I couldn't believe I became a "senior member" so quickly. If you click on the symbol above the posting, on the left, with I think a question mark and a face, you can get more info about the person who posted, including how many times they've posted and when they joined the board. That can give you a better idea of how long someone has been around, if you're curious.