​What Does the Term Point of Unsaturation Mean

​What does the term point of unsaturation mean?

A) the area on a fatty acid chain where the carbon bond is holding a hydrogen
B) the area on a fatty acid chain where a nitrogen is attached
C) ​the area on a fatty acid chain where a hydrogen is missing from the bond
D) the area on a fatty acid chain where there is a zig-zag formation
E) ​the area on a fatty acid chain where carbon forms a double bond with oxygen