What does it mean for something to be "inter-ethnic?"

Does inter-ethnic refer to things that are between different ethnic groups, or within one ethnic group?

If it refers to things that are between different ethnic groups, what word would be used to refer to things that are within one ethnic group?

Inter means between. The Latin prefix for within is intra. However I wouldn't use "intra-ethnic" -- in fact I can't think of a sentence which would refer to "things within one ethnic group". One might talk perhaps of "inter-ethnic conflict", but "intra-ethnic conflict"? I think not: it would be "ethnic Europeans (for example) are fighting amongst themselves".

Google Books has 28,000 hits for intra-ethnic plus 15,000 for intraethnic, so it's not particularly unusual. Given intra- is a common, productive prefix signifying inside, within, interior, during, I disagree with Andrew's advice here to avoid the term completely. Though like the majority of those writers, I would avoid the unhyphenated version because it's a little tricky to read correctly at first glance.