What and when is the calender Q4? The only information I've found about it says it is near the holiday buying season but I don't know when that is either.
Firms tend to divide their trading periods into quarters. If your reading a UK annual report, then Q4 will begin from january to end of march, as the business year tends to start and end in april due to the tax man, if its an american company their tax year starts and ends in january.