is carbon double bound the reason why alkenes are unsaturated What exactly does it mean to be unsaturated

Yes, the carbon double bond is the reason why alkenes are considered "unsaturated".

In chemistry, the term "unsaturated" refers to a molecule that contains fewer hydrogen atoms than the maximum possible amount. In the case of alkenes, the carbon atoms in the double bond are not fully saturated with hydrogen atoms, as they would be in an alkane. This means that alkenes have the potential to react with other molecules to form new bonds and increase their hydrogen content, making them more stable.

The double bond in alkenes also gives them unique properties, such as the ability to undergo addition reactions and act as nucleophiles or electrophiles