What is Ramadan?

Ramadan is the ninth month of the Islamic calendar, when Muslims fast during daylight hours.
There are several reasons why Ramadan is considered important:

• The Qur'an was first revealed during this month
• The gates of Heaven are open
• The gates of Hell are closed and the devils are chained up in Hell.

The Qur'an revealed

The actual night that the Qur'an was revealed to the Prophet Muhammad is called Lailat ul Qadr, and to stand in prayer on this one night is said to be better than a thousand months of worship.
Ramadan is often called 'month of the Qur'an' because of this, and Muslims attempt to recite as much of the Qur'an as they can during the month. Most mosques will recite one thirtieth of the Qur'an each night during the Taraweeh prayers.
No one knows on which particular night the Qur'an was first revealed, but it is said to be one of the last ten nights of Ramadan.

The gates of Heaven are open and the gates of Hell are closed

Muslims believe that their good actions bring a greater reward during this month than at any other time of year, because this month has been blessed by Allah.
They also believe that it is easier to do good in this month because the devils have been chained in Hell, and so can't tempt believers. This doesn't mean that Muslims will not behave badly, but that any evil that they do comes from within themselves, without additional encouragement from Satan.
Almost all Muslims try to give up bad habits during Ramadan, and some will try to become better Muslims by praying more or reading the Qur'an.
 
Muslims believe that this is one way that the chaining up of the devils is manifested, since there is no other reason for them to do so.