Major sins are defined as what is forbidden by Allah & His messenger in the Qur'an & the Sunnah in addition to what is narrated on the authority of early Muslims. Allah, the most High, promises whoever avoids the major sins to expiate his minor sins. Allah, the Almighty says,

{If ye (but) eschew the most heinous of the things which ye are forbidden to do, we shall remit your evil deeds, & admit you to a gate of great honour.}
Al-Qur'an surah Nisaa: 31

In this text, Allah the most High, also promises whoever avoids the major sins to admit him to paradise.
Allah, the Almighty says,
{Those who avoid the greater sins and indecencies, and when they are angry even they forgive;}
Al-Qur'an surah Ash-Shura: 37
The Qur'an also states,
{Those who avoid great sins and indecent deeds, save lesser offences, verily thy Lord is ample in forgiveness.}. Al-Qur'an surah An-Najm:32

The prophet (pbuh) said,
"The five prescribed Prayers, and from one Friday Prayer to another and from Ramadan to another entail forgiveness for what is between them as long as you do not commit the major sins."

We are obliged to learn about what the major sins are, so that Muslims may avoid them.

Let us use this thread to share our knowledge on what are the different kind of Major sins to avoid.
May Allah help us.