What is tayammum and in what cases is it performed?

Islam is a religion of convenience 
In such cases, the palms of both hands will be thrown to the ground or to the stone, and applied to the face and back of both hands is equivalent to wodu or ablution.

Instead of ablution (Wudu) or ghusl, I should perform tayammum:

1. Water is not available

2- Water is harmful for the body

  3- The time for prayer should be so short that there is no opportunity for ghusl or ablution

  4- The water should be in such a way that if it is used for ablution or ghusl, there is a risk of death

  5- Preparing water is life-threatening

  6- Water should be enough to wash your body or C

7- The water is usurped.