What Is Osu And How Do I Know One When I See Him/her?

A very close friend of mine who has been dating an igbo guy for over 6 years now, infact they ve been engaged hoping to get married very soon, they traveled last week for introduction but my friend called me last night crying her eyes out on the phone, i even managed to hear what she was saying

Her fiance's people did not approve of the marriage, the guy's family said over their dead body will their son marry my friend (because they said shes an OSU)

My friend never knew she was an osu (thats if theres anything like that) shes going crazy over this issue because she and the guy are madly inlove, now they plan to run out of the country to get married and raise their own family.

I am confused and don't know what advise to give my friend for now because I don't know what OSU is and the implications it comes with.

Please my fellow Igbo Brothers and sisters, can anyone explain to me what OSU is, I leanrt its a traditional thing,how can you tell if someone is an OSU and most importantly what should be a Christian's view about this OSU thing please?

another osu thread . . .
. . hiiiisssssssssssssssssssssssssssssssssssssssssssssssssss