Big O notation has attained superstar status among the other concepts of math because of programmers like to use it in discussions about algorithms (and for good reason). It’s a quick way to talk about algorithm time complexity.
While it’s a math concept that applies to various fields, programmers are probably one of the most frequent users of Big O. We use it as a shorthand to discuss how quickly and/or with how much memory an algorithm takes to go from start to finish.
Perhaps the part about Big O being most used by programmers is just my carpal-tunnel-visioned mind speaking, but nevertheless! It’s an important concept and here’s a post dedicated to understanding the Big O notation.