What is ontology gas used for?

Ontology Gas, also known as ONG, is a utility token within the Ontology blockchain ecosystem. But what exactly is it used for? As a questioner, I'm curious to know the various functions and applications of Ontology Gas. Does it play a role in transactions? Does it power smart contracts? Or is it used for governance and staking purposes? I'd like to gain a deeper understanding of the importance and versatility of Ontology Gas within the Ontology blockchain platform.