Compiler optimization is a process used by compilers to improve the performance and efficiency of the code they generate. By analyzing the source code, the compiler can make changes that reduce execution time, memory usage, or both. This can involve simplifying complex expressions, eliminating redundant calculations, or rearranging instructions to make better use of the computer's resources. There are various techniques for compiler optimization, including constant folding, dead code elimination, and loop unrolling. These techniques help create faster and more efficient programs without altering the original functionality, allowing developers to deliver better-performing applications with less effort.