My friend has a B-1/B-2 MULTIPLE INDEFINITELY (American) visa. What kind of a visa is that?

Question

There is such a visa. It writes on his passport!

Answer 1

Sorry, but there is no such thing as a US "B-1/B-2 multiple indefinitely" visa.  

A B-1/B-2 visa means the holder is visiting the US for (limited) business and/or pleasure; multiple (entry) means the holder is eligible to seek entry at a US port of entry more than once, up to the final day of the visa's validity; and in terms of validity, the very most a US visa will have is a ten-year validity, based on international reciprocity - the expiration date is printed on the visa itself.

Answer 2

It's a tourist visa.  Your friend cannot lawfully hold a job and must leave by the date stamped on his/her I-94 that was issued at the time he/she entered the United States.