The IRS has industry classification codes used for statistical analysis. These codes have varied over the years, but now use SIC (Standard Industrial Codes) that are the same from one agency to another.
But over 30 years ago, when I was a newbie tax examiner for the IRS, we used to get a good laugh from prostitute's returns--yes many DID file--where prostitution was legal--certain Nevada counties. Anyway, sometimes we'd give them business codes like "Meat Wholesaler", "Personal Services--Other", "Entertainer", and my favorite: "Freelance Journalist".