"Hands down" means "without a doubt, 100% certain" It's usually used in informal settings, like conversations between friends or online, and rarely in formal settings like business or academia. Example: "Spanish is spoken in 21 countries and has more than 500 million speakers, you should learn it hands down"

hands down can also be a synonym for "absolutely" or another meaning is "easily or without much effort." EX. It was hands down, the funniest movie I have ever seen. (Here, absolutely or Joe's synonyms work perfectly)