How can we stop it?
There's no real way to actually completely squash terrorism but we can make small steps towards it. For one we need to stop supporting the dictators who fund terrorists. Saudi Arabia is the world's largest sponsor of radical Islamic terrorists. We also could stop mass surveillance, it makes us more vulnerable.
What is terrorism?
terrorism is the use of violence and intimidation in the pursuit of political aims. The FBI uses this definition "Terrorism is the unlawful use of force and violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives."