Cheshvan (or Mar-Cheshvan) is the eighth of the twelve months of the Jewish calendar.

In the Bible, Cheshvan is called chodesh bul, from the word mabul, "the flood." The flood began on the 17th of Cheshvan, and ended the following year on the 27th of Cheshvan. The following day, the 28th of Cheshvan, Noah brought his sacrifice to G-d and G-d swore never again to bring a flood upon the earth to destroy all mankind, and then revealed the sign of His covenant with the world, the rainbow.

Cheshvan is the only month which has no holidays or special mitzvot.We are taught that it is "reserved" for the time of Mashiach, who will inaugurate the third Temple in Cheshvan.
 

http://www.inner.org/times/cheshvan/cheshvan.htm
 

Kay