The original definition of terrorism is "government by intimidation"[1]. i.e. If a government uses terror to control it's populace, it's terrorism, e.g., U.S. government intimidating it's workers not to whistle-blow is one example. Somewhere along history it flipped to "intimidation of governments". Whichever way you read the word, however, the U.S. is a state sponsor of terrorism[2], having provided support to Al-Qaeda and Bin Laden when they were fighting in Afghanistan against the Soviet Union, amongst many others[3][4], not withstanding the acts causing terror such as the bombing of a Doctors Without Borders hospital[5], and in 2013 giving weapons to Syrian Rebels[6], which we know ISIS & Al-Qaeda[7] are the biggest factions.
To answer your question, Pinochet, Taiwan government in 70's, Stalin, would all be terrorists, according to the original definition of terrorism, as in "intimidation by governments". Somewhere along the way propaganda completely reversed the meaning of the word to "intimidation of governments by non-government actors". Either way, the word "terrorism" used in propaganda everywhere, it is a loaded word used carefully with craft to manipulate the people's perception of nefarious activities performed by governments from all around the world, the biggest of which is the U.S. government.
Terrorism, the word itself, is the weapon.
Terrorism are certain activities performed by one's enemies, when one wishes to use the word terrorism to intimidate the populace to allow the government to implement draconian policies.
1. http://www.theguardian.com/world/2001/may/07/terrorism
2. https://en.wikipedia.org/wiki/Allegations_of_CIA_assistance_...
3. https://en.wikipedia.org/wiki/United_States_and_state-sponso...
4. https://en.wikipedia.org/wiki/Raymond_Allen_Davis_incident
5. http://foreignpolicy.com/2015/10/05/us-bombs-doctors-without...
6. https://www.washingtonpost.com/world/national-security/cia-b...
7. http://www.telegraph.co.uk/news/worldnews/middleeast/syria/1...
U.S. claims to only supply weapons to "moderate" rebels, and U.S. describes Al-Qaeda as "moderate".