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 concept of a "notebook" or "book of biji" refers to a genre of writing that originated during the Wei and Jin dynasties and flourished in the Tang dynasty. It is characterized by its diverse content, including anecdotes, quotations, personal reflections, scholarly discussions, and literary critiques.