It roughly translates to "notebook". A book of biji can contain anecdotes, quotations, random musings, philological speculations, literary criticism and indeed everything that the author deems worth recording. The genre first appeared during the Wei and Jin dynasties, and matured during the Tang dynasty.
The term "notebook" roughly translates to "book of biji."  Biji books are filled with various types of content, including anecdotes, quotes, personal reflections, scholarly discussions, and literary critiques. This genre originated during the Wei and Jin dynasties and reached its peak in the Tang dynasty.