Definitions for "Fansub"
fan-subtitled video (by fans for fans).
A fan-subtitled production. This is the only way to find a translation of many less popular titles, as well as a few surprising ones like Rayearth. Often done with amateur equipment and/or unprofessional translation. Generally these are distributed by copying freely, so poor quality copies are common. It is unethical as well as illegal to fansub a show which is being commercially translated. It is also highly unethical to "bootleg" (sell for profit) fansubs.
Fansubs are anime that are translated and subtitled by fans. This is usually done for anime that have not been commercially licensed outside of Japan, and is a way for fans to view anime that they normally wouldn't get a chance to see. While fansubs are technically illegal, they are usually tolerated by companies as long as the titles have not been commercially licensed and are distributed on a non-profit basis.