GitLab CI is a continuous integration tool built into the GitLab platform, designed to automate the software development process. It allows developers to run tests and build their code automatically whenever changes are made, ensuring that new code integrates smoothly with existing code. This helps catch errors early and improves overall code quality. With GitLab CI, users can define pipelines using a simple configuration file called `.gitlab-ci.yml`. This file specifies the stages of the pipeline, such as build, test, and deploy, along with the scripts to execute at each stage. This automation streamlines development workflows and enhances collaboration among team members.