The Equalization edit panel view is used to display and edit equalization frames for the current file selection. The intent of these items is to redefine an equalization curve within the audio file. There can be more than one Equalization item in a file but each description field should be non empty and unique.
The table displays the equalization items found in the currently selected files.
A equalization items has a Description field which is a short description used to differentiate multiple items in the same file. This field is intended to be unique amongst all the items in a single file.
All editing and manipulation is done via the context menu and is described here.
The format of an Equalization frame (EQU2) can be found in the ID3 specification available here: id3.org
It is extremely doubtful that you would ever have to use these items or that you would encounter them in files. They are included for completeness.