Terrorism is unlawful use of violence or the threat of violence to attain goals that are religious, political, ideological, economic, etc. in nature to inculcate fear; intended to coerce or to intimidate governments or societies in the pursuit of said goals.
One of the more obvious recent examples of this are the 9-11 atrocities. Another is the US-Contra war on Nicaragua. After the ICJ condemned the US for the "unlawful use of force", US Southern Command gave the contras (mostly former members of the Somoza regime) the first official orders to attack what they called "soft targets" (read undefended civilian targets). That's a textbook example of international terrorism. Even before the ICJ ruling, the contras were attacking civilians. The Contras were fighting to reverse the popular sandinista revolution. This is an example of the unlawful use of violence to attain goals that are political and ideological. Saddam Hussein's invasion is an example of international terrorism. CLinton's bombing of a Sudanese pharmaceutical plant is another. And we can go down the list. The point is that the US govt, and most other govts around the world use terror to get what they want. Clearly, overwhelmingly, terrorism is the weapon of the strong.