Regulation S-K is a prescribed regulation under the US Securities Act of 1933 that lays out reporting requirements for various SEC filings used by public companies. Companies are also often called issuers (issuing or contemplating issuing shares), filers (entities that must file reports with the SEC) or registrants (entities that must register (usually shares) with the SEC). Regulation S-K is generally focused on qualitative descriptions while the related Regulation S-X focuses on financial statements.