A double bond is a covalent bond in which two pairs of electrons are shared between two atoms. It is stronger and shorter than a single bond and, because it contains a pi bond, does not allow free rotation. The O=O bond in oxygen (O₂) is a double bond.

双键是两个原子之间共享两对电子的共价键。它比单键更强、更短,且因含有一个 π 键而不允许自由旋转。氧(O₂)中的 O=O 键就是双键。