Sunni and Shi'a
Do you know who the Sunnis and who the Shiites are? Take this quiz and find out if you know more about what's going on in the Middle East than most Congressmen do.
FWIW, I got 8 out of 8, but it was a hard 8 out of 8. I wasn't 100% certain of the answers to at least two questions.
While I'm on the topic, do you know how Islam split into these two competing sects? The split came about due to a disagreement about who should succeed Muhammad and how that successor should be chosen. Muhammad died without formally naming a successor. After Muhammad's death, a meeting was held on the issue and Abu Bakr, Muhammad's father-in-law, was chosen to lead the Muslims.
According to Sunni Muslims, this was proper and thus Abu Bakr is the first of Muhammad's successors (caliphs). According to the Shi'a, there was some foul play and intimidation afoot to prevent Muhammad's, and Allah's, true, chosen successor, Muhammad's cousin and son-in-law Ali, from taking over. They believe that only Allah can choose the successor, and thus, even though Abu Bakr was chosen by consensus, it was illegitimate, and Ali is therefore the true first caliph.
This all happened in the 7th century CE.
While the West tends to see both as "Muslims" and part of the same religion, Sunni and Shi'a don't necessarily see it that way. Just as some fundamentalists in the US believe that Catholics (and often other protestants) aren't Christians, in Sunni-dominated Saudi Arabia Shi'a aren't considered Muslims at all.
Just preachin' a little information at ya.