400 BAD request HTTP error code meaning

Question

I am posting a JSON request to an HTTP URL.
Should this be treated as 400 where: the requested resource field exists but "Roman" is an invalid value for this field?

[{requestedResource:"Roman"}]

Should this be treated as 400 where the "blah" field doesn't exist at all?

[{blah:"Roman"}]

Any help would be appreciated.