Advanced Package Tool (APT) is a free, open source software package management system used to install, update, remove, and manage packages in Linux and Unix-like operating systems. It is primarily used as a command-line tool, but it can also be used as a graphical package manager in some Linux distributions. APT is a replacement for the original Debian package manager, dpkg. It can be used to quickly and reliably install, remove, and upgrade packages on a system, and can manage dependencies between packages. It is also used to manage software repositories, which can be hosted locally or remotely. APT also offers additional features such as installing packages from multiple sources, downloading packages from the Internet, and more.
It is in the same operating system, for the same packages.