Double Click means to dig one level deeper into the data: to open the detail behind a summarized number and see what it is made of.
The term borrows the computer gesture of double-clicking to open something. In accounting software it is often literal. In 📝Quickbooks Online, for example, running a 📝Profit and Loss Statement shows one total per account; clicking an amount opens a report of the individual transactions behind it, where a miscoded vendor or a missing entry becomes visible.
Used figuratively, a request to double click on a result is a request to go beneath the summary, from a total to its accounts, from an account to its transactions, or from a metric to the drivers that produce it. It is the move behind drilling deeper into results to understand deeper drivers, one of the 📝Financial Planning and Analysis functions.