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, and Debian-based 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 code