What does the E in ESXi stand for?

What does the E in ESXi stand for?

• Evolution
• Elastic
• Enterprise
• Electronic 

EXPLANATION

After version 4.1 (released in 2010), VMware renamed ESX to ESXi. ESXi replaces Service Console (a rudimentary operating system) with a more closely integrated OS. ESX/ESXi is the primary component in the VMware Infrastructure software suite. The name ESX originated as an abbreviation of Elastic Sky X