10-K (Annual Report)

A Form 10-K is the comprehensive annual report that domestic public companies file with the Securities and Exchange Commission. It contains audited financial statements, management's discussion and analysis, risk factors, and disclosure about the business, its properties and its legal proceedings. Foreign private issuers do not file a 10-K. They file an annual report on Form 20-F, or on Form 40-F under the multijurisdictional disclosure system available to certain Canadian issuers.

The 10-K is the most complete financial disclosure a public company makes — written for investors and regulators, not for marketing.

What this tells you

The annual report a US public company files with the SEC — the most complete document a company produces: audited financial statements, the business description, risk factors, and management's own discussion of results.

What it does not tell you

It is annual, so it arrives long after most of what it describes. And it contains no separate fourth quarter — the 10-K covers the full year, and Q4 has to be derived from it, which works for figures that add and not for per-share figures. Risk factors are also written by lawyers to be comprehensive rather than predictive. Almost every risk that could conceivably matter is disclosed by almost every company, which makes the section thorough and nearly useless for distinguishing one company from another.

Further reading: Wikipedia