Tanbi is no longer written. Tanbi is a word meaning 'the worship and pursuit of beauty'. It was used to describe the early male/male stories that mainly ran in June. June was heavily influenced by a well-known author and literary critic who used multiple pen names, so many of the stories utilized a high literary style. These stories came to be called tanbi - stories written for beauty and pursuit of beauty only. Tanbi style includes flowery language and uncommon kanji/words, which makes it a difficult read for foreigners.
The tanbi style is mainly a thing of the past. It has been replaced by BL stories - mass written, easy-to-read stories. Even authors known for their tanbi works like Yoshihara Rieko (Ai no Kusabi) now write mainstream BL and no longer use tanbi style. It's probably because tanbi, like its name, pursues beauty both in language and storyline. It's not simple and fast-paced like the modern BL stories.
Tanbi is like shounen ai, no longer written but important in the evolution of modern BL.
Tanbi sometimes is used interchangeably with boys' love by bookstores, but that's an old usage.
Ai no Kusabi was lovely.