A pi bond is a type of covalent bond that occurs when two atomic orbitals overlap sideways. This bond typically forms in addition to a sigma bond, which is the first bond between two atoms. Pi bonds are found in molecules with double or triple bonds, such as in ethylene (C2H4) or acetylene (C2H2). They contribute to the overall stability and reactivity of these molecules. In a pi bond, the electron density is concentrated above and below the plane of the bonded atoms, rather than directly between them. This unique arrangement allows for certain properties, such as restricted rotation around the bond axis. Pi bonds play a crucial role in the structure and behavior of many organic compounds, influencing their chemical reactions and physical properties.