What is the apple disk image in disk utility, and how can I delete it?

I am using Early 2015 MacBook Air and I am trying to re-install my Mac and when I go to Disk Utility after Command + R Recovery mode, There is an additional drive than Macintosh HD.

There is a drive under "Disk Images" called "Apple disk image Media" with "OS X Base System" under it, using 1.27 GB with 728 MB free. How do I delete this Disk Image drive?

I have re-installed Mac multiple times, I have never seen this disk image before.