What does the CT suffix stand for in voltage regulator?
Part number suffixes are decided somewhat arbitrarily by each manufacturer. Often the refer to either different temperature ranges the parts are specified over, or to the package the part is provided in.

But in this case, the part is only available in one package (TO-220), and with one suffix (CT), so there's no way to know. Nor does it really matter, since you can't choose any other suffix from this vendor.

Maybe by looking at other Fairchild parts, you could find a pattern. Second source parts from other manufacturers will have different suffixes, so their datasheets won't help you know what the Fairchild suffix means.

If there were different suffixes available, you would usually be able to work out their meaning from the "Ordering Information" table, on page 1 of the dataseheet in this case. For example, if you look at the Fairchild KA78xx datasheet, you'll see that for that part family an "ETU" suffix indicates TO-220 package, while "RTF" or "RTM" suffix indicates DPAK.