A comprehensive summary report of a company's performance that must be submitted annually to the Securities and Exchange Commission. Typically, the 10-K contains much more detail than the annual report. It includes information such as company history, organizational structure, equity, holdings, earnings per share, subsidiaries, etc.
Taobiz explains 10-K
The 10-K must be filed within 60 days (it used to be 90 days) after the end of the fiscal year.
10-K = Yearly
10-Q = Quarterly