These compounds are unsaturated fatty acids, although they are rarely found in natural lipids (fats, waxes, phospholipids, etc.).
A double bond is said to be at position k if it connects carbons k and k+1 of the chain, counting from 1 at the carboxyl end.
The systematic name of the acid is formed by prefixing the positions of the double bonds to "decadienoic" or inserting them before the "dienoic" suffix.
However, geometric isomerism may still occur at that position in derivative compounds where one or both terminal hydrogens are replaced by different groups.
Geometric isomerism raises the number of decadienoic acids with separate double bonds from 21 to 72, and of those with an allene core from 6 to 11.