Some media reports use the term to describe "holdover" or "overwintering" fires, which burn underground in the off-season and flare up again when conditions permit.

https://www.king5.com/mobile/article/tech/science/environment/what-are-zombie-wildfires-can-they-happen-in-pnw/281-4076bb77-e636-4c5e-becd-e8e29e732aa0