Well, the other definitions pretty much hit it on the nose.
But don't be like the junior high retards and pronounce it "EXANGA". Them, along with many dumbasses who use Xanga actually are stupid enough that they pronounce the "X" in Xanga to make it sound like "EXANGA". The "X" in "Xanga" is pronounce as a "Z". Pronounced "Zanga". Although middle school retards who are obsessed with Xanga can't even wrap their minds around the pronunciation even though they were taught how to pronounce "X" as a "Z" in the beginning of words in elementary school.
You don't call someone named Xander, "EXANDER".
You don't pronounce the word "Xylophone" as "EXylophone"
"X" used that as first letter in words is pronounced as a "Z"