These terms are often used in articles which explore conflicts and war. They are confusing terms, so I thought I should write up some more definitions as they are worth knowing! The terms listsed here have been ‘inspired by’ articles by Sambanis, and Alan Collins book on Contemporary Security Studies.
Intrastate: Intrastate violence is the most common form of conflict today. It describes sustained political violence that takes place between armed groups representing the state, and one or more non-state groups. Violence of this sort usually is confined within the borders of a single state, but usually has significant international dimensions and holds the risk of spilling over into bordering states (the current conflict in Syria would be described as a Intrastate conflict).
Interstate: Interstate violence is a conflict between two or more states (both members of the international system), who use their respective national forces in the conflict.
Extrastate: Extrastate conflict is between a state (member of the international system) and a political entity which does not come in the form of a recognized state. This type of conflict can take place outside the boundaries of the state recognized by the international community.
Hope this helps! 🙂