A Global field is a reusable field (consisting of a group of fields) that you can define once and reuse in any content type within your stack. This field saves the time and effort of adding the same set of fields (and their settings) in multiple content types of a stack.
This field possesses certain properties that you can change any time as per your needs. The properties that can be modified are “Select Global Field,” “Display Name,” “Unique ID,” “Instruction Value,” “Help Text,” “Multiple,” and “Non-localizable.”
An example of this field would be creating the SEO field. When you create an SEO global field, add and configure a few subfields (“Meta Title” and “Meta Description”) under it. Now, you can add this global field to multiple content types of your stack.
Then, while creating an entry, this SEO field will be automatically populated with the Meta Title and Meta Description subfields, as shown below: