I've found that "Spider" is a program that automatically fetches Web pages, that means that someone is visiting MS trough such program.
"Junior member" - I'm not sure where have you seen that?
"Invisible" - means that such member has chosen to be invisible for others while he is on line at MS. It is possible to adjust this option if you go to My stuff and than Edit preferences - there is question Hide from Who's Online?
I hope some other experienced members would help with additional answers....