The term "heavy hitter" is an idiomatic expression that refers to a person or thing that is exceptionally impressive, influential, powerful, or successful. It can be used in various contexts such as business, sports, politics, and entertainment to describe someone who stands out from the rest due to their achievements, abilities, or reputation. In other words, it's a term of admiration for those who are at the top of their game and have made significant impacts in their respective fields.