It is a document filed by a company to the Securities and Exchange Commission (SEC) who wants to sell new issues (shares) to the public. Referred to as Red Herring only sometimes.
There is no details about issue price or the size of the issue in the red herring prospectus. It is not the final prospectus and it is updated many times.
It is just an indication that the company wants to issue new securities to the public and it will not attempt to sell its securities before the registration is approved by the SEC.