Plugin editor is a simple text editor which is used to edit a plugin you wish to edit. It allows users to view and edit plugin files from within your WordPress admin area. Plugin editor has a text area where it opens the plugin files. There is a drop down menu on the top that allows you to select a plugin that you want to edit.
At this point you should only use this section if you know what you are doing. You should note that any changes that you make directly into your plugin’s core files will be overridden when you update the plugin. In theory, you should never be using the plugin editor to edit any files. Often developers use the built-in editor to view the code to make appropriate changes by utilizing a hook or filter within the plugin.
Unlike the the Theme Editor, if you make a syntax error in your plugin editor, then it won’t lock you out of your WordPress admin. It will simply deactivate the plugin and explain the error to you.
What is WordPress Plugins?
Plugins you must have as a WordPress Beginner
Step by Step to Install a WordPress Plugin