You might already know about general wait listing process in railways. It is represented by W/L followed by a number which represents your waitlist number. A W/L doesn’t grant you permission to board a train but a RAC does, which is the middle stage between W/L and a confirmed berth.
The above terminology applies if you booked a ticket in General quota. In case you booked your ticket under Tatkal quota and unfortunately get a waitlisted ticket, it will be indicated as CKWL followed by a number. Similar to General quota,
RAC follows CKWL (there is no RAC in tatkal; from WL you will either directly get a confirmed berth or remain in WL). A CKWL status after the chart is prepared bars you from boarding the train. In such cases, the passenger will get his ticket price back, minus some transactional charges.
Under tatkal quota CKWL is very common since the ticket purchase happens very fast, especially in busy routes (starting at 10 am). Even though you see tickets status as available, after making your payment you may end up in the waitlist, since there are only few tickets under tatkal quota and many passengers trying to grab them, all at the same time.
Normally speaking, a General quota waitlist ticket has greater chances of getting confirmed than a tatkal ticket. This is even more pronounced in those trains which don’t have good number of berths allotted to tatkal quota.
Note: If you want me to tell if your WL ticket gets cleared or not, please mention the train number (or name), names of the station from where you board and get down, class of travel and date of travel. Better yet, just tell me your PNR number. It will automatically tell all the above details (and just those). I will edit out the PNR number (even though I think it is not something that is sensitive) just in case you mind.
Note 2: I will only monitor the comments once or twice a day, so if you have some thing urgent (like your train leaving in a few hours and you want to know your status), please use the contact form link above or message on facebook (like box on the right).