Jewish Holidays aka Yamin Tovim are the holidays or good days that the Jewish people spend in observance of their Judaism. Jews have their own Hebrew calendar which is composed from 3 main sources Jewish History, Rabbinic Mandates, and Biblical Mitzvot. There are 6 mandates from the hebrew bible know as the Yom Tov. These 6 dates are holidays where all activity is strictly prohited and known as Shabbat. The only work allowed is food prep. The 6 days are the first and last days of Passover, the first day of Shavout, Rosh Hashanah, the first days of Shemini Arzeret, Sukkot, Yom Yov Sheni Shel Galuyot, and Yom Kippur.
Melacha is what the Jewish people refer to as the translation of work. The jewish people have a number one rule of refraining from Melacha on certain holidays. Melacha is Jewish law. This law contains thirty nine sections of labor that were performed when they constructed the Tabernacle. Melacha is not restricted on all Jewish holidays but just for a select few.
There is only one exception to Melacha when a holiday prohibits it and that is the labour in which is required to save a life. The hebrew language refers to saving a life as Pikuach Nefesh. The Jewish people take this very serious. They do not bat an eyelash when it comes to Pikauch Nefesh and will violate Shabbat immediately in order to save a life without feeling any shame.
The Torah tells the Hewbrew calendar the dates for the Jewish people to preform their holidays on. If the holiday is specifically of biblical origination then the Jewish people will spend two days observing their holiday out side of the land of Israel. Then they will celebrate for the next two days inside the land of Israel. The only exception to this rule is Shabbat and Yom Kippur. The months are lunar on the Jewish calendar.