Shavuot (Hebrew שבועות), ("[seven] weeks") (pronounced: shah-voo-OH-t) is one of the three Biblical pilgrimage festivals; it is a major Jewish holiday; it is also known as the Feast of Weeks. Greek-speaking Jews gave it the name Pentecost (πεντηκόστη) since it occurs fifty days after Passover. If you don't count Passover, the holiday is 49 days after Passover, which is a jubilee of days. This ends the Counting of the Omer.
Shavuot has many aspects and as a consequence has been called by many names. In the Hebrew Bible it is called the "Feast of Harvest" (Hebrew: חג הקציר, Hag ha-Katsir; Ex. xxiii. 16) and the "Feast of Weeks" (Hebrew: חג שבעות, Hag Shavuot; ib. xxxiv. 22; Deut. xvi. 10), also the "Day of the First-Fruits" (Hebrew יום הבכורים, Yom ha-Bikkurim; Num. xxviii. 26).
Connection with harvest
In ancient Israel the grain harvest lasted seven weeks and was a season of gladness (Jer. v. 24; Deut. xvi. 9; Isa. ix. 2). It began with the harvesting of the barley during the Passover and ended with the harvesting of the wheat at Shavuot. Shavuot was thus the concluding festival of the grain harvest, just as the eighth day of Sukkot (Tabernacles) was the concluding festival of the fruit harvest. According to Ex. 34:18-26, Shavuot is the second of the three festivals to be celebrated at the sanctuary. The Israelites are to bring to the sanctuary "the first-fruits of wheat harvest," "the first-fruits of thy labors which thou hast sown in the field." These are not offerings definitely prescribed for the community; "but with a tribute of a free-will offering of thine hand . . . shall you rejoice before the Lord yout God, you and your son and daughter,.. the Levite that is within your gates, and the stranger, and the fatherless, and the widow" (Deut. xvi. 9-12). In Lev. xxiii. 15-22 there is a regularly appointed first-fruit offering which the whole community must bring. Various animal sacrifices were enjoined, and no work was permitted.
In Rabbinical literature
The festival is known in the Mishnah and Talmud as Atzeret. This term is usually translated a "solemn assembly," meaning the congregation at the pilgrimage festivals. The name is applied also to Passover (Deut. xvi. 8) and to Sukkot (Lev. xxiii. 36). In post-Talmudic and geonic literature the Biblical name Shavuot was resumed.
Shavuot falls on the 6th of Sivan and never occurs on Tuesday, Thursday, or Saturday. In many communities outside Israel, the holiday is celebrated for two days.
Shavuot is the fiftieth day of 'Omer (counting of the grain offering). During the existence of the Temple in Jerusalem the first-fruits were offered as well as a sacrifice of two loaves of bread from the new harvest, etc. (Lev. xxiii. 15-21).
"The morrow after Sabbath"
Regarding the Biblical commandment to offer the 'omer "on the morrow after the Sabbath" = (ib. verse 11), the ancient scholarly rabbis maintained that "Sabbath" here means simply a day of rest and refers to Passover. The Sadducees (Boethusians) disputed this interpretation, contending that "Sabbath" meant "Saturday." Accordingly they would transfer the count of "seven weeks" from the morrow of the first Saturday in Passover, so that Pentecost would always fall on Sunday. The Boethusians advanced the argument "because Moses, as a friend of the Israelites, wished to give them an extended holy day by annexing Pentecost to the Sabbath." Johanan then turned to his disciples and pointed out that the Law purposely fixed the interval of fifty days in order to explain that the seven weeks, nominally, do not necessarily begin from Sunday (Men. 65a, b). See also Pharisees.
The traditional festival of Pentecost as the birthday of the Torah (i.e. "the time our Law was given"), when Israel became a constitutional body and "a distinguished people," remained the sole celebration after the Exile. The Shavuot prayers have references to this and particularly to the precepts deduced from the Torah. Kabbalists (adherents of Kabbalah, esoteric Jewish mysticism) arranged a special service for the eve of Shavuot, consisting of excerpts from the beginning and end of every book of the Bible and Mishnah, which abridgment they considered tantamount to the reading of the complete works, and accepted as the approval of the Law.
Tikkun Lel Shavuot
The reading occupies the pious till morning; others finish it at midnight. The collection is called Tikkun Lel Shavuot ("Preparation for Pentecost Eve"). The Pentateuch reading contains three to seven verses from the beginning and the end of every parashah (or sidra). Some of the important sections are read in full, as follows: the days of Creation (Gen. i. 1-ii. 3); the Exodus and the song at the Red Sea (Ex. xiv. 1-xv. 27); the giving of the Decalogue on Mount Sinai (ib. xviii. 1-xx. 26, xxiv. 1-18, xxxiv. 27-35; Deut. v. 1-vi. 9); the historical review and part of Shema (ib. x. 12-xi. 25). The same method is used with the excerpts from the Prophets: the important ch. i. of Ezekiel (the Merkabah) is read in full. The Minor Prophets are considered as one book: the excerpts are from Hos. i.1-3, Hab. ii. 20-iii. 19, and Mal. iii. 22-24 (A. V. iv. 4-6). Ruth is read in full; and of the Psalms, Ps. i., xix., lxviii., cxix., cl. The order of the twenty-four books of the Scriptures is different from the accepted one: probably it is an ancient order, as follows: (Torah) Five Books of Moses; (Prophets) Joshua, Judges, Samuel, Kings, Isaiah, Jeremiah, Ezekiel; (Minor Prophets) [Hagiographa] Ruth, Psalms, Job, Proverbs, Ecclesiastes, Song of Solomon, Lamentations, Daniel, Esther, Chronicles, Ezra: all from the 24 books. Next, the excerpts from mishnayyot are read, the beginning and end of every treatise, in all sixty-three, with some important chapters in extenso; next, the Sefer Yeẓirah; the 613 precepts as enumerated by Maimonides (see Commandments, The 613). Later, excerpts from the Zohar bearing on the subject were added, with opening and concluding prayers. The whole reading is divided into thirteen parts, after each of which a Ḳaddish di-Rabbanan is recited.
The Zohar calls the time between Passover and Pentecost the "courting days of the bridegroom Israel with the bride Torah." Those who participate in the tiḳḳun celebration are the Temple-men meaning those "of the King [God]." The Zohar has two epigrams on Pentecost: (1) "In the twin month [zodiac sign of Gemini] the twin Law [written and oral] was given to the children of twin Israel [Jacob and Esau]." (2) "In the third month Sivan the treble Law [Pentateuch, Prophets, and Hagiographa] was given to the third [best] people" (Zohar, Yitro, 78b).
Because the Law was given on Pentecost, the Rabbis wished to make that day the most enjoyable holy day. R. Joseph ordered a third (best) calf for the festival, saying: "Were it not for this day how many Josephs would there be in the street!" ("without the Law there would be no distinction of scholarship," Pes. 68b). A popular custom on Pentecost is to eat dairy foods and cheese-cakes in honor of the Law, which is likened to "honey and milk" (Cant.iv. 11). The meat meal follows the milk meal. These two meals represent the two loaves of bread, formerly offered in the bikkurim offering at the Temple service.
In the synagogue the scroll of Ruth is read because the story of Ruth embracing Judaism and the description of the scene of harvesting are appropriate to the festival of the Law and of the harvest. Another reason given is that King David, a descendant of Ruth, died on Pentecost (Sha'are Teshubah to Oraḥ Ḥayyim, 494).
Floral decorations and confirmation
The custom widely prevails of displaying greens on the floors and of otherwise decorating the home and the synagogue with plants, flowers, and even with trees. The greens serve to remind one of the green mountain of Sinai; the trees, of the judgment day for fruit-trees on Pentecost (R. H. i. 2); they also commemorate the harvest festival of former times.
Confirmation in Reform Judaism
In an effort to encourage assimilation and end anti-Semitism, many Reform Jews in Europe in the 1800s promoted ending many traditional Jewish rituals, and adopting new rituals based on those of their Protestant Christian neighbors. As such, they created what they called the rite of confirmation for 16 year old Jewish boys and girls in the synagogue on Shavuot. This spread to Reform Judaism in America. This ritual in many communities replaced the celebration of Bar mitzvah for some time; in the last 30 years most of the Reform movement has readopted the traditional observance of the Bar or Bat mitzvah; confirmation ceremonies are now more rare.
Date of the giving of the law
Within the Jewish tradition, the exact day on which the Torah was given is in dispute. Most of the classical rabbis say it was given on the 6th of Sivan; according to R. Jose it was the 7th of that month. The classical rabbinic literature holds that the Israelites arrived at the wilderness of Sinai on the new moon (Ex. xix. 1), and that the Ten Commandments were given on the following Saturday. The question whether the new-moon day fell on Sunday or Monday is undecided (Talmud, tractate Shabbat 86b).