Package Manager vs Dependency Manager

TLTR: Package Manager is used for SYSTEM and Dependency Manager for PROJECT

Package Manager - is used to configure system, ie to setup your development environment and with these settings you can build many projects.

Dependency Manager - Is specific to project. You manage all dependencies for a single project and those dependencies are going to be saved on your project. When you start another project you should manage your dependencies again.

EXAMPLE: In PHP world there is COMPOSER as dependency manager and PEAR as package manager. When using composer all your settings and extensions are for single project where pear settings to setup new extension and library to php core.

There is an excellent and simple explanation on Composer's website:

Composer is not a package manager in the same sense as Yum or Apt are. Yes, it deals with "packages" or libraries, but it manages them on a per-project basis, installing them in a directory (e.g. vendor) inside your project. By default it does not install anything globally. Thus, it is a dependency manager.