Rokkasen (six famous poets) (六歌仙)
Rokkasen are the following six poets that KI no Tsurayuki remarked as "poets of the best known of recent times" and commented on the style of poetry of each in "Kokin Wakashu Kanajo" (Preface of Kokin wakashu written in kana):
ARIWARA no Narihira
FUNYA no Yasuhide
ONO no Komachi
OTOMO no Kuronushi
"Rokkasen" is, however, the term that was given later.
KI no tsurayuki merely listed the names of renowned modern poets, so there was no common style of poetry among them. These six poets belonged to the years decades prior to the days of compilers of Kokin Wakashu (Collection of Ancient and Modern Japanese Poetry), so poems in the collection are divided into three periods: Period of Unknown Poets, Period of Rokkasen, and Period of Compilers.
Kokin Wakashu Kanajo (relevant part only)
In Kokin Wakashu Kanajo, KAKINOMOTO no Hitomaro and YAMABE no Akahito are remarked as Great Poets with special treatment; on the other hand, Rokkasen poets were evaluated as far inferior to two Great Poets, as described above. Poets other than Rokkasen were, however, regarded as too worse to refer to (There are others as well who are known, as numerous as the leaves of the trees of the forest, as widespread as the ivy which crawls in the fields, but they think anything they compose is poetry and do not know what poems are.), thus Rokkasen poets were valued as worth reviewing.
The term Rokkasen is diverted to refer to a group of one woman and five men. The most famous group was Tenpo Rokkasen in a story of the same title known by Kodan storytelling or Kyogen (farce played during a Noh play cycle) by Mokuami KAWATAKE.