Definition:
In Software Development, build is a process to compile source into binary code, packaging binary code and running automated test. In build process there are steps repeatable, executed in a specific order which is automated using build script or tools at any time is a automated build.
There are different types of build automation servers, On-demand automation where developer runs build script at the command line, Scheduled automation server which is a continuous integration server running a nightly build and Triggered automation server where continuous integration server runs a build on every commit to a version control system.
The advantages of build automation to software development projects includes a necessary precondition for Continuous Integration (CI), Continuous Testing and Continuous Deployment (CD) improving product quality, accelerating the compiling and integration process, eliminating redundant tasks, eliminating dependencies on key personnel and having history of builds and releases in order to investigate issues.
Further Reading:
Book: Continuous Delivery: Reliable Software Releases through Build, Test, and Deployment
Automation Jez Humble, David Farley
Book: Blameless Continuous Integration: A Small Step Towards Psychological Safety of
Agile Teams by Vivek Ganesan