The common definition of terrorism is the systematic use or threatened, use of violence to ultimate the population of government and there by effect political, religious, ideology change.
motives of terrorism : 
1. The motivation of terrorist are quiet various depending on what they hope to accomplish. 
2. The majority of motives can be broken down into the three broad areas rational psychological and cultural events.
3. Although some motives are difficult for the majority of the world to comprehend given a motive a terrorist group.