Private vs. Public Side
The private side of the investment bank encompasses groups that have access to inside company information that is not available to the public. It is separated from the public side by the “Chinese wall” (this is not a joke; it is the actual expression in the industry).
The private side is known as the investment banking side of the business. This includes both industry and product groups.
These groups are dealing directly with the company/government and have access to all inside information. Note that bankers on the private side of the business are strictly prohibited from using any of that knowledge for their own benefit or the benefit of others. So whenever you hear there was some case of insider trading, that means that some type of private information was leaked and someone took advantage of it.
The public side has access only to information that average Joe has access to (e.g. information found in the annual reports, SEC filings, etc.). This side includes S&T and equity research. Although these professionals work in the same building with investment bankers, they are not exposed to private information. There are strict regulations within every bank controlling that their S&T and research staff does not take advantage of that information. Therefore, employees take this very seriously.