What is object manager in Magento 2?

Object manager is Maento 2 core class a “Magento/Framework/ObjectManagerInterface”.

Object manager to avoid boilerplate code when composing objects during instantiation.

In the Magento framework, the implementation of the ObjectManagerInterface performs the duties of an object manager.

Responsibilities :

The object manager has the following responsibilities:

1. Object creation in factories and proxies.
2. Implementing the singleton pattern by returning the same shared instance of a class when requested
3. Dependency management by instantiating the preferred class when a constructor requests its interface
4. Automatically instantiating parameters in class constructors