RE offered the Bullet Electra in different varaints. The ES with the Electra stands for the 'electric start' whereas the term 5S was used for describing the 5 speed gearbox in the Bullet. The older models of the Bullet generally had a 4 speed gearbox and the Electra was the first Bullet to get a 5-speed gearbox. Also it had the option of electric start, which was missing in the Standard variant.

Quick Facts - Royal Enfield Bullet Electra