Most companies have a fiscal year end around December 31, so their fiscal years and periods line up with normal calendar years and periods. However, for companies that have other fiscal year end dates, there will often be a difference between the calendar and fiscal period and year.
In Calcbench, we allow you to look at data based its best fitting calendar period, in order to make it more comparable across company. For example, calendar period Q4 2013 contains data from each company that best fits the period from October to December 2013. For most companies this will also be their fiscal period Q4 2013. However, in the case of Apple (AAPL), whose fiscal year ends in September, calendar period Q4 2013 would line up with Apple's fiscal period Q1 2014 (the period from November to December 2013).
In addition, companies that do not have periods ending at the end of December, may assign their fiscal year however they see fit. One company might consider themselves to be in fiscal year 2014, when another similar firm may consider themselves to be in fiscal year 2013. In order to compensate for this, we assign a standard calendar year. If a company's year ends on or before June 30, 2014 they are in calendar year 2013. If it ends after, they are in calendar year 2014.
TTM (or trailing twelve months) means that we are adding up the quarters necessary to show a full year's worth of financials ending at the specified calendar period.
Assigning fiscal periods to calendar periods follows this logic - If the midpoint of the period falls in the first 91 days of the year it get sets to Calendar Q1. With the exception being retailers and other companies that follow the 4/4/5 calendar and have unusual length periods, we sometimes have adjust those on a case by case basis.