An ESD, Electronic Software Download, file is an encrypted file used for Windows installation as stated here:
so the file itself is called a Windows Electronic Software Download file. An ESD file stores an encrypted Windows Imaging Format (.WIM) file.
Your PC has downloaded (or is downloading) that the file(s) to upgrade Windows. But they could also be used to reset your PC as described here:
These ESD files are used for “resetting your PC” to its factory default settings. If you delete these files, you’ll have more disk space–but you won’t have the files necessary to reset your PC. You may need to download Windows 10 installation media if you ever want to reset it.