A reset CSS file is a set of styles that sets the default values for various elements on a web page to a consistent baseline. The purpose of a reset CSS file is to provide a consistent starting point for styling web pages, so that different browsers display elements consistently and so that you don't have to spend time undoing default browser styles.
Normalize CSS, on the other hand, is a set of styles that makes default styles consistent across different browsers, but does not completely reset all styles to a baseline like a reset CSS file does. The goal of normalize CSS is to make it easier to style web pages consistently across different browsers, without completely eliminating the default styles of those browsers.
In summary, a reset CSS file completely resets the default styles of a web page to a consistent baseline, while normalize CSS makes default styles consistent across different browsers without completely resetting them.