Organic compounds mean carbon compounds. Carbon is unique element in the periodic table. It has 4 valence electrons. That means each individual carbon atom can bind to 4 other atoms of almost any variety and each of those 4 can bind to 4 others atoms. This leads to formation of organic compounds having incredible variety and complexity - short chains, long chains, ring structures, branched structures and so on.This self linking property of carbon atom is called catenation, which leads to existance of very large number of carbon compound.