ordinary book; mediocre writing; commonplace handwriting
Refers to a book of no special merit, or to handwriting that is unremarkable and ordinary. Often used in contrast to 良書 (good book) or 名筆 (fine handwriting).
This library has many ordinary books, so it's hard to find what you're looking for.
彼の字は凡書で、特に上手というわけではない。
His handwriting is just ordinary; it's not particularly skillful.