ACV = apple cider vinegar rinse. It is the final step to the wash/condition process. The ACV is a porosity stabling device nad it closes the cuticle in order lock in moisture. Your hair should be stronger, shinier, and ph-balanced afterwards. For me, I could tell the difference instantly-- my hair after wash detangling was easier and hair was noticeably stronger. If you want to know more about acv rinses there are tons of threads w/testimonials and more info-- just do a search