"Liquid smoke" is a seasoning made from condensing the smoke of burning wood. It is used to add a smoky flavor to food without actually smoking it. Full definition
The only change I made was to add about 1/2 cup of diced onion and 1 teaspoon of liquid smoke. (allrecipes.com)
I'm not a fan of anything smoked, but totally understand the need for liquid smoke in certain recipes, like this one. (connoisseurusveg.com)
In a measuring cup, measure out water; add liquid smoke directly to the cup and stir (this way the smoke will be evenly distributed). (hellyeahitsvegan.com)