A ratio is just what it sounds like - A ratio of your amount uploaded divided by your amount downloaded.
If you achieve a share ratio of 1:1, that would mean you've uploaded as much as you've downloaded. This is typically a minimun acceptable result. The higher the number, the more you have contributed. While share ratings are just displayed for your convenience, courtesy to others should cause you to keep this ratio as high as possible in the event you need to prove you're not a leecher.
May I have an invite to Oink? I can post a pic of my share ratio.