Here’s the Wikipedia article on them: https://www.wikiwand.com/en/articles/Electrolyte
For simplicity’s sake, they are salts, acid, or bases that can suspend themselves in a polar liquid, like water, and can conduct electricity.
They help maintain the body’s ability to hydrate, and are critical in maintaining nerve and muscle functions, since they are electric tissues.
Between this and the EPA regulation rollbacks, were going to see a whole lot of bloody dead Americans.