Now really, would you think that these are all the same thing?
Well, you could get some techy argument here and there: somebody
might insist that iCal should refer only to the Mac OS X app
of that name and not to the iCalendar internet standard, and that
neither one should be used to describe the underlying file format
(vCalendar). But in common usage, it's all the same. That Mozilla picked Sunbird for their app's name is about the only thing that isn't all
cross-pollinated and confused.
The data files Sunbird, Mac's iCal and any other conforming
calendar app use are simple text files that look like this: