A Linux distribution (often called a distro for short) is an operating system made as a software collection based on the Linux kernel. All distros have the kernel, a packet manager like APT on Debian based systems and RPM on Red Hat based systems. Distros also have a default desktop environment like Unity for Ubuntu and Cinnamon  for Linux Mint. Each distro comes with a collection of open-source or proprietary software pre-installed. There are maybe thousands of Linux distributions but Mint and Ubuntu are by far the most popular.