Nisan is the first month of the ecclesiastical year and the seventh month (eighth, in leap year) of the civil year in the Hebrew calendar. Nisan has 30 Days in it. In the TaNaCH it is called Aviv which means spring. In the Book of Esther (also part of the TaNaCH) it is called Nisan.
Holidays During The Month
Fast of the Firstborn — 14th Nisan (or 12th Nisan when the 14th falls on Shabbat)
Passover — 15th through 21st Nisan (22nd outside Israel)
Yom HaShoah — 27th Nisan (National observance in Israel, 26th Nisan or 28th Nisan when the 27th falls on Friday or Sunday, interfering with Shabbat)
Counting the Omer — 16th Nisan through 5th Sivan
Special Shabbat During The Month
- Shabbat HaGadol