Which statement accurately describes an alkene?

An alkene is characterized as an unsaturated hydrocarbon, which means it contains at least one double bond between carbon atoms. This double bond is what distinguishes alkenes from alkanes, which are saturated hydrocarbons and consist only of single bonds. The presence of a double bond in alkenes allows for additional reactivity compared to their saturated counterparts, making them an important class of compounds in organic chemistry.

The correct answer highlights this defining feature—being unsaturated with at least one double bond—allowing alkenes to participate in various chemical reactions that are not possible for saturated compounds. Understanding this aspect is essential in recognizing the structure and reactivity patterns of alkenes in organic reactions.