影印 is a formal term for photocopying or photo-offset printing, mostly used in academic publishing and archival contexts. As a verb it means to make a photocopy or photographic reproduction; as a noun it refers to the copy itself. In everyday speech most learners will encounter 复印 (fùyìn) for simple photocopying, but 影印 carries a slightly more technical feel — think of reproducing rare books or documents.