Conversational is social interaction, just chatting away. various mistakes and lack of knowledge can be glossed over. Doesn't work so well when doing business and trying to part a client from their money.
Business level requires specialist vocabulary in order to conduct business effectively. In Japan it would probably also mean mastery of various keigo. Indeed apparently nowadays Japanese are taught keigo as part of inductions into companies.
I'd also expect you'd have knowledge of how business is conducted in Japan.
There's even a JLPT like test for business Japanese.
http://www.jetro.go.jp/en/bjt/
The usual scale for language skills is more akin to that adopted by the European Union for
Europass where you rate practical abilities in the four major skills.
Where it matters for a job you are at least likely to be tested at interview on your language claims. A native speaker will probably be able to get a sense your ability fairly quickly.