It just means employees of businesses that were able to continue operation during the pandemic lockdowns. Iirc, being a source of sustenance enabled fast food/takeout to remain open. Regardless of the nutritional value offered.

That’s how “essential worker” included both medical professionals and fast food. It is also how certain call centers were still crammed with people unless remote was made available. The phrase was seemingly used to help improve morale for those forced to work while benefits for the unemployed paid out more than their wages.

“Essential worker” just means non-union poors, realistically. If you’ve got no leverage and don’t make enough to have any savings, you are required to continue going to work no matter what happens.