noun
pi electron
Technical term in physics and chemistry; refers to an electron in a pi bond or pi molecular orbital.
ベンゼン環には6個のπ電子が非局在化している。
In the benzene ring, six pi electrons are delocalized.
σ電子 (sigma electron) refers to electrons in sigma bonds, contrasting with π電子 which are in pi bonds.
Compound of パイ (pi, from the Greek letter π) and 電子 (でんし, electron). The term is a direct calque from English 'pi electron'.