Answer Description
APT (Advanced Packaging Tool) is the default package manager for the Ubuntu Linux distribution. A package manager is a system used to download, install, update and remove software applications.
Wikipedia
Advanced Package Tool, or APT, is a free-software user interface that works with core libraries to handle the installation and removal of software on Debian, Ubuntu, and related Linux distributions. APT simplifies the process of managing software on Unix-like computer systems by automating the retrieval, configuration and installation of software packages, either from precompiled files or by compiling source …
APT (Debian) - Wikipedia, the free encyclopedia