Answer
Constitutional isomers.
Work Step by Step
They are constitutional isomers. The molecular formula of both the compounds is $C_5H_{10}$. The constitutional isomers may differ in ways other than the branching of their carbon chain. They may differ in the position of a double bond like in the case of these two compounds. On the left one the double bond is between the first and second carbon, and on the second one the double bond is between the second and the third one.
