GNU Make is a build automation tool that helps manage and maintain groups of programs and files. It uses a file called a "Makefile" to define rules and dependencies, allowing users to specify how to compile and link their code efficiently. When a user runs Make, it checks the timestamps of files to determine which parts of the project need to be updated. This process saves time by only rebuilding what is necessary, making it especially useful for large software projects where recompiling everything would be inefficient.