#What-I-Wish-My-Christian-and-Atheist-and-Generally-Non-Jewish-Friends-Knew-about-Judaism Vol. 3 is the first in a few posts about the Shabbat, that will be posted on Fridays.
Yes, I can already hear some of you gasp, "Oh my, you spelled Sabbath wrong!" Actually, I didn't. The word "שבת" is pronounced, and thus transliterated as "shabbat". The stem of this word is "shavat", meaning "ceasing", that is, from work. I personally think that translating it as rest is incorrect: it doesn't imply rest, and the Shabbat is not primarily a day of rest. The English word "Sabath" was derived, possibly by a reading mistake, from the Hebrew word.
Shabbat denotes the seventh day of the week, based on the creation story found in Genesis. Isaac Asimov also wrote an essay about how weeks came to exist, which is a pretty non-Bible based, but absolutely possible approach.

Since the Shabbat is such a dominant part of the lives of Jews, we have special greetings we use on this day. Starting somewhere around midday Friday it's apropriate to greet someone with "Shabbat Shalom". Another greeting is "Shalom aleichem", meaning peace unto you. The response to that is "Aleichem shalom."
Shabbat is often referred to as "Shabbat haMalka", Shabbat the Queen. Shabbat is this special for us. Of course the levels of observance vary among Jews just as much as keeping the Sabath holy vaaries among Christians. There are two basic things that all the Shabbat mitzvot (laws) come down to: to enjoy and sanctify it.
If you have any questions, feel free to ask. It's a lot easier for me to write about things that my readers would like to know.