Buddhism was a religion originated in Old Earth's Indian subcontinent around the 27th Century Ante Diaspora. Its followers were known as Buddhists.
Throughout its thousands of years of history, the Buddhist religion became practiced throughout the worlds of the Diaspora, including the Star Kingdom of Manticore.
The astrogator of the superdreadnought HMS Manticore at the time of Honor Harrington's service onboard that ship was a Buddhist. (HH5)