In general, a Gherkin Editor is a text editor that allows you to write feature files using Gherkin syntax.
Gherkin is a "Business Readable" language created especially for behavior descriptions. Its simplicity allows non-technical users to write specifications and it also allows you to remove logic details from behavior tests. Gherkin serves two purposes: serving as your project's specification/documentation and automated tests.
The SpecFlow Gherkin Editor gives you additional tools to assist you in writing better Gherkin and also gives you the ability to share Gherkin feature files so you can collaborate with your team more easily.