What does "omnibus" mean?

An omnibus is a collection of literary works by a single author, or works by multiple authors centered on a single theme. More rarely, it is used as a legal term to refer to a document that addresses or proposes numerous items at the same time.

Literary omnibus editions usually contain reprints of previous work, including collections of two or more book-length works; multiple short essays, poems or stories; or a single longer work and several short works. Omnibuses dedicated to a single author may collect that writer's best-known pieces, work from a specific period in his career or all works that share a common genre or character.