In layman’s terms, what is a flat white?

I’ve been a barista for almost 8 years and have never worked at a place that made a flat white. Someone told me that it requires a speciality grinder and I just ran with it lol. I tell people that we don’t have the equipment to make a flat white and suggest latte. 90% they opt for latte or cappuccino instead. People and Google tell me different things and use jargon that I can’t process. I want to know to better explain and upsell. Thanks!