Refers to the act of rewriting or the rewritten text itself; often implies improvement or correction. 書き直し is the noun form of 書き直す.
I was ordered to rewrite the report.
This manuscript needs rewriting.
書き直し means a rewrite or revision of existing text, whereas 書き下ろし means an entirely new work written from scratch for a specific release.
Compound of 書き (continuative form of 書く 'to write') + 直し (continuative form of 直す 'to fix, correct').