8-K (Current Report)

An 8-K is a report public companies must file with the SEC to announce major events shareholders should know about — including earnings announcements, executive changes, acquisitions, guidance revisions, and other material events.

The 8-K is the market's breaking news wire for public companies — when something material happens, it must be filed within 4 business days: guidance revisions, dilutive offerings, restatements, and executive changes.

What this tells you

The current report — filed when something happens that shareholders should know about promptly, rather than on a quarterly schedule. Earnings releases, executive changes, material agreements, acquisitions, auditor changes.

What it does not tell you

An 8-K announcing earnings is a press release attached to a filing. The figures in it are management's presentation of the quarter and are frequently not the same as the audited or reviewed figures that appear in the 10-Q weeks later — and the differences tend to be exactly where management had the most latitude. It also has no fixed schedule, so its absence means nothing. A company with no recent 8-K may have had a quiet quarter or may simply have judged nothing reportable.

Further reading: Wikipedia