Build automation is the practice of having a program, rather than a person, carry out the steps that turn source code into something you can run or ship. Those steps usually include compiling source files, linking or assembling them, running tests, and packaging the result into a deliverable artifact. The goal is that anyone can reproduce the same build by running one command, instead of remembering a sequence of manual steps.
The earliest widely used build tool was Make, which let a developer describe targets and the commands needed to produce them. Make worked well for C programs but tied builds to the host platform’s shell and command-line tools. The Apache Ant FAQ describes this pain directly for Java: developers were “struggling with Makefiles” before Ant arrived to give Java projects a portable way to build (https://ant.apache.org/faq.html).
Later tools added more than just running commands. Apache Maven introduced a declarative project model so that, in its own words, it “is able to build any number of projects into predefined output types such as a JAR, WAR, or distribution based on metadata about the project, without the need to do any scripting in most cases” (https://maven.apache.org/what-is-maven.html). Maven also folded in dependency management, fetching required libraries automatically.
Modern build tools such as Gradle extend this further with incremental builds, where only the parts of a project affected by a change are rebuilt. Across this whole history, the core idea stays the same: capture the build process in code so it is repeatable, shareable, and not dependent on one person’s memory.