What is fieldset in Salesforce?

A field set is a grouping of fields for an object. Creating field sets in Salesforce is an easy way to dynamically query fields and dynamically binding the fields to display field sets on your Visualforce pages which can save you a big chunk of time. Field set is an out of the box feature provided by Salesforce and you can create field sets for Standard as well as custom objects and supports the inclusion of custom and Standard fields.