I don't know. What is the difference between a member, a junior member, and a senior member? And this better be funny!
Intellect, writing prowess and general superiority in all of life's myriad aspects exponentially increases as one's membership-rank increases... Actually, it is based on your post count. Don't know the exact numbers.
What Mammamaia said. Its just a title the forum gives you after a certain amounts of posts. From the looks of it Senior Member is like a 100 posts or so.
If you are green like me, it's cause you been here that long you ended up turning moldy. bahahahahahaha! ;-)
It might be noted that there's another sort of member: the banned one. And while the other designations say nothing about the bearer's insight or expertise, if a member is banned - and you may perhaps happen upon their ghastly outpourings in a resurrected thread - be clear on this: what they say is often vile and always wrong.