Let's see the how the git website defines git, it's pretty straight forward and self explanatory:

Git is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.

But, wait a minute, what is a VERSION CONTROL SYSTEM ???

VCS (Version Control System)

Let's see how microsoft's website explains what a version control system is:

Version control systems are software that help track changes make in code over time.

But why do I need a version control system???

Need of VCS

Without version control, developers are tempted to keep multiple copies of code on their computer. This is dangerous because it's easy to change or delete a file in the wrong copy of code, potentially losing work. Version control systems solve this problem by managing all versions of the code, but presenting the team with a single version at a time.