Short version: ACF, or Advanced Custom Fields, is a WordPress plugin used to add structured custom fields to editing screens.
In plain language, ACF lets a website owner or editor fill in specific pieces of content instead of placing everything into one free-form editor. A field group can define inputs such as a hero subtitle, product detail, case study metric, related service, FAQ answer, team role, or glossary metadata. Those fields can then be displayed by the theme, a template, Elementor, or custom code.
ACF is useful when a site needs consistency across repeated content types. For example, every case study can have the same fields for client, problem, solution, result, and industry. That structure makes content easier to maintain and reduces layout mistakes, while the visual template still controls how the information appears on the public page.
Related terms: WordPress, custom post type, and CMS.