"Backed" usually means "redeemable for."

Energy (aka electricity, aka compute) is what makes rewrites of the public information costly, which is part of Bitcoin's security model.

Bitcoin is not an "energy coin" though. If it would be, you could print endless bitcoin with a fusion reactor. Also, think about why a coin minted in 2010, a coin that required very little energy to be minted (according to your mental model) is equal in worth to a coin minted now, with energy requirements that are a gajillion times higher.