Composer - Dependency Manager for PHP

Composer is an application-level dependency manager for the PHP programming language that provides a standard format for managing dependencies of PHP software and required libraries.

Composer runs from the command line and installs dependencies (e.g. libraries) for an application. It also allows users to install PHP applications that are available on “Packagist” which is its main repository containing available packages. It also provides autoload capabilities for libraries that specify autoload information to ease usage of third-party code.

Composer is not a package manager in the same sense as Yum or Apt are. It manages them on a per-project basis, installing them in a directory inside the project. By default, it does not install anything globally. Thus, it is a dependency manager. It can support a “global” project for convenience via the global command.

Composer in Magento

Composer enables you to manage Magento components and their dependencies, providing you with the following advantages over a ZIP install:

Enables you to reuse third-party libraries without bundling them with source code
Component-based architecture with robust dependency management
Semantic versioning
Supports the PHP Framework Interoperability standard