ROS stands for Robotic Operating System. It is a framework of different tools such as an abstraction layer, libraries, and a package manager that makes it easier to program/interface with different robotic systems/components. It basically simplifies a lot of work that you would be doing on your own. While it is extremely useful, it also has some flaws. For example, it is bloated, can be tricky to configure, and can be sometimes difficult in making it do what you want it to.