Welcome to the forums marykcrawford.
Perhaps you meant “area” limitations? Commercially made dvds have regional restrictions, and if you have one that was intended for another area, it will not work in your player. Wikipedia’s entry on dvd regional codes can explain this better than I can in this thread: http://en.wikipedia.org/wiki/DVD_region_codes
And you may be looking at different formats. Most countries around the world use PAL format for dvd-video. The US, Canada and a few others use NTSC. The two standards differ on resolution of the video and frame rate.
There are many options for dealing with this. You can sometimes find a hack for your stand alone player that allows it to become region free. You can also rip the dvd to the hard drive of your computer, and remove the restrictions. You’ll need dvd decryption software for that, like DVDFab or AnyDVD. Once on the hard drive you can then burn to a new, blank dvd, but depending on the size of the video you might need to compress, or use a double layer blank dvd.