Geisha: a woman trained as an entertainer in the Japanese tradition.
Geisha were taught to sing, play instruments, dance compose and recite poetry, pour tea and other drinks, etc. Men paid to spend time with the geisha; generally, the transaction did not include sexual services.
Traditionally, girls began training as geisha when they were as young as four or five years old. Today, they begin as teenagers, and become full-fledged geisha in their early twenties.
Geisha became popular in the late eighteenth century. They lost status during the early twentieth century, as the line between geisha and prostitutes blurred, but today the profession is respectable again (and highly popular with tourists).
The word "geisha" comes from gei meaning "arts" and sha or "person" - so literally, a geisha is simply an artist.
See a gallery of geisha images here, both photographs and woodblock prints.