EXIF data refers to the exchangeable image file format used for supplementing images with rich metadata, such as the equipment used to take a shot (manufacturer and model), orientation and exposure, color space and dimensions, location where the image was captured, and so forth. I suspect that it's that last bit -- location -- that many people worry about.
A number of Mac software titles allow you to read, write and edit photo metadata, most obviously iPhoto. You can view and update EXIF data in iPhoto's floating Info palette.
If you don't mind working at the command line, Auntie's favorite solution is ExifTool, a Perl-based utility that provides a simple way to retrieve, modify or strip data. Removing GPS information from a photo proves as simple as exiftool -geotag= IMG_1297.jpg. Can't get any easier than that.
Other EXIF solutions for the Mac include Reveal from Album Shaper and ExifRenamer from Qdev, although Auntie has not used either product herself.
With the proper tool, you can fake dates and locations just as easily as you can strip data to protect your privacy. So regardless of which tool you use, remember to use your powers for good not evil. Because Auntie will be watching.
Best of luck!