what is diaster, refer to IT environment?

Answer 1

A disaster is when you lose your important data, in a disk crash, a fire, flood, by malicious activities, non malicious stupidity, etc.

The key is what you plan to do in the event of a disaster.

Answer 2

A disaster in IT is when you can't log into World of Warcraft!

But otherwise you could consider flooding, electrical spikes, frequent network downtime, fire, data theft, data destruction, virus attack.

Practically any natural disaster is an IT disaster, along with any theft of interlectual property, and you need to plan for all of that.