The MD5 hash of the $1text parameter, or the $1prependtext and $1appendtext parameters concatenated. If set, the edit won't be done unless the hash is correct.
MediaWiki:Apihelp-edit-param-md5
From Froggitt
The MD5 hash of the $1text parameter, or the $1prependtext and $1appendtext parameters concatenated. If set, the edit won't be done unless the hash is correct.
