Basically, it is a subcategory of ethnic conflict (not all ethnic conflict is ethno-national conflict, but all ethno-national conflict is ethnic conflict).

The conflict (whether political, military, or terrorist) may be contained within a particular country, but it's often played out in disputed regions or territories. For example, there are many ethnic groups that see themselves as "nations" but are not be recognized as such by the international community (Palestine) or the governments that control those areas (Tibet). Some related issues/drivers include separatist movements, disputed territories, ethnic minority oppression, colonial/post-war boundary lines that don't match the historical and cultural history of a region, etc.

This article contains many good examples:
http://www.slate.com/id/2258127/

http://en.wikipedia.org/wiki/Ethnic_group#Ethno-national_con...
Sometimes ethnic groups are subject to prejudicial attitudes and actions by the state or its constituents. In the twentieth century, people began to argue that conflicts among ethnic groups or between members of an ethnic group and the state can and should be resolved in one of two ways. Some, like Jürgen Habermas and Bruce Barry, have argued that the legitimacy of modern states must be based on a notion of political rights of autonomous individual subjects. According to this view, the state should not acknowledge ethnic, national or racial identity but rather instead enforce political and legal equality of all individuals. Others, like Charles Taylor and Will Kymlicka, argue that the notion of the autonomous individual is itself a cultural construct. According to this view, states must recognize ethnic identity and develop processes through which the particular needs of ethnic groups can be accommodated within the boundaries of the nation-state.

The nineteenth century saw the development of the political ideology of ethnic nationalism, when the concept of race was tied to nationalism, first by German theorists including Johann Gottfried von Herder. Instances of societies focusing on ethnic ties, arguably to the exclusion of history or historical context, have resulted in the justification of nationalist goals. Two periods frequently cited as examples of this are the nineteenth century consolidation and expansion of the German Empire and the twentieth century Third (Greater German) Reich. Each promoted the pan-ethnic idea that these governments were only acquiring lands that had always been inhabited by ethnic Germans. The history of late-comers to the nation-state model, such as those arising in the Near East and south-eastern Europe out of the dissolution of the Ottoman and Austro-Hungarian Empires, as well as those arising out of the former USSR, is marked by inter-ethnic conflicts. Such conflicts usually occur within multi-ethnic states, as opposed to between them, as in other regions of the world. Thus, the conflicts are often misleadingly labelled and characterized as civil wars when they are inter-ethnic conflicts in a multi-ethnic state.