Wash is the finished product of fermentation that is destined to be distilled for the first time. It is a term used in the production of almost all distilled beverages that are made from scratch (although most overheard in Whisky and Rum).
It’s worth noting that there’s a huge crossover between wash and wort, and that while different, for all essence and purposes, they are used very interchangeably by many distillers. For the pedants like ourselves however… to clarify: Wort technically becomes Wash as soon as yeast is added to start fermentation (even if the term is usually used to refer to the liquid at the end of the fermentation).