Pi Bond (ฯ): The second kind of bonding that occurs when orbitals overlap on their sides, forming one part of multiple bonds such as double bonds.
Sigma Bond (ฯ): The first kind of interatomic bonding that forms from end-on overlapping orbitals, present in all types of covalent bonds including single and multiple ones.
Resonance Structures: Different ways to represent molecules with multiple bonds that cannot be depicted by one simple Lewis structure.