What actually is terrorism and why is it dangerous?

Today I'd like to touch upon such a topic of current interest as terrorism. Really nowadays we hear this term on the Internet and TV all the time but actually cannot give it a comprehensive definition. But if we ponder over thet issue a little bit we'll find out that the only basic characteristic of terrorism generally agreed upon is that it involves violence or the threat of violence. Generally speaking, each act of terrorism is a well-staged perfomance devised to have a strong influence on the society, government or the stability in the whole country.
The main aim of terrorists is to shake the foundation of the country. Sometimes terrorism may be based on some kind of ideology or may serve to achieve some political or ideologicsl ends. Personally I'm inclined to believe that some religions are more likely to provide basis for different kind of terrorist and extremist movements. It doesn't mean that they're worse or more violent , not a word about it! It just means that they might be misinterpreted somehow in order to alter the main idea. It's not a secret that Islam created a great variety of terrorist organizations including notorious Al-Qaeda and ISIS. And all these organizations, to a large extent, are the consequonces of one misinterpreted islamic principle: Jihad or sacred war against pagans.
And also I'd like to share my opinion on the difference between the terms ''terrorism'' and ''extremism''. Terrorism, as I've mentioned above, usually involves acts of physical violence. A suicide-bomber blows up himself in the middle of the crowd or hijakers ram skyscrapers like it was on 9.11 — all this implies direct physical agression. Talking about extremism we need to use another approach because it uses non-physical tools and instruments to mobilize minds to achieve political and ideological ends. For instance, the current iranian regime is called extremist because of its totally islamic basis. Nevertheless, Saudi Arabia which is also a state based on islamic principles is not considered to be an extremist one. So, the limits of these terms are very blurred and unclear. Sometimes it's rather hard to distinguish them properly.
To conclude... Fortunately the international community agrees on the fact that terrorism is dangerous and it's a common priority to combat it. And such an acknowledgement adds some stability to our fluctuating world.