What is tribbing? have you ever heard of it?

I texted my girlfriend the other day cause she was over a friends house and wanted to know when she was coming home. She said that her and her friend were tribbing until her friends boyfriend came home and then she would be home. I asked her what she meant and she just said lol never mind you wouldn't want to know. then that got me thinking of course and I kept asking her but she wouldn't tell me and just said I shouldn't have said that just never mind it. Anybody know what this means?

what the f***? are you kidding me?

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