Scanlation is a portmanteau of "scanning" and "translation." It refers to the process by which fans scan physical copies of manga, translate the original Japanese text into another language (typically English), digitally edit the translated text into the speech bubbles, and distribute the finished product online. This practice is nearly always conducted without permission from the copyright holder and exists in a legal grey area.
The translation and distribution of "comic lo translated work" exist in a complex ethical and legal space.