An Ajah of the Aes Sedai. The Brown Ajah forsakes the mundane world and dedicates itself to seeking knowledge. The head of the Brown Ajah is Jesse Bilal.
NS,Ch12 - The Brown Ajah quarters in the White Tower are plainly decorated compared to other Ajahs.
NS,Ch14 - The Blue Ajah is also a bit at odds with the White and Yellow over something in Altara a hundred years before. The Brown Ajah supports the White against the Blue, but supports the Blue against the Yellow.
The Eye of the World,Glossary - The purpose of the Brown Ajah is given. It "forsakes involvement in the mundane world and dedicates itself to seeking knowledge."