Accounting data file created by the Mac version of QuickBooks, a small business accounting program; contains company financial management information, such as income and expenses; used for tracking financial data, as well as filing taxes. Mac versions of QuickBooks use the software year as part of the file extension. For example, the QuickBooks 2009 extension is .QB2009. NOTE: QB2006 files were used for a previous tax year, so they are now considered legacy.