"Day of rest", from the Hebrew word Shabbat. Shabbat literally translates as "the seventh day" but means "the day of rest." The seventh or last day of the week. The first sabbath was the "day" God rested after having completed the creation in six "days", according to Genesis 2:2-3
Early Christians honored the Sabbath on Saturday, the seventh day, which continued until the publication of the first blue law by Constantine in the 4th century A.D., Sunday became the Christian Sabbath.
A few Christian sects, notably the Seventh-Day Adventists, currently honor the Sabbath on Saturday, but most use Sunday.
Some people believe Acts 20:7 holds evidence that Paul worshipped on Sunday as the "new Sabbath. One must remember, according to Jewish tradition and as expressed in the Bible, a day begins when the sun goes down. This means that this meeting was held on what we know as Saturday night. That would make the next morning and afternoon the second part of the first day. Surely we know that Paul would not have walked eighteen miles from Traos to Assos on the first day if it had been the new holy day. Much less then boarded a boat and continue to travel to Mitylene and finally on to Chios. Paul was a lifelong Sabbath keeper and if the first day was now the Sabbath, this journey would have been contrary to his character. Paul actually was keeping Sabbath by waiting until the first day to continue his “work“.
People also mention that the breaking of bread proves that a communion service was held. In Mat. 14:19 Christ broke bread to feed the multitudes, even though there is no mention of communion or Sabbath. Also it tells us in Acts 2:46 that they went to the Temple and broke bread from house to house "daily". Again there is no mention of communion or Sabbath. The final conviction that some have with these verses is that Paul was preaching on this day. There are many instances of the gospel being taught and preached on non-specific days as well as daily. One example is in Mark 2:1-2 another is Luke 19:47-20:1 where it clearly indicates that Christ himself taught and preached daily. There is no significance given to the day, the breaking of bread, nor the preaching, they are merely mentioned. The focus of the story is about Eutychus, his accident, and his resurrection.
Sabbath is also used to non-religiously refer to the heavy metal band Black Sabbath.