What is "fresh" yeast? How does it differ from dried yeast and where would one procure it. Alternately, how would you substitute for it if unable...

Fresh yeast is yeast in a moist cake-like form, usually found in the refrigerator case at the store since it can't be stored on the shelf. Use to be available in supermarkets and still is in certain areas, but I haven't seen it in the supermarket since the 80's. Here's a conversion table for substituting dry yeast if you can't procure the fresh stuff,
http://www.redstaryeast.com/lessons-yeast-baking/yeast-conversion-table