WYSIWYG is an acronym for What You See Is What You Get.
WYSIWYG is a way of designing electronic documents so that content such as text and graphics is displayed on screen during editing in a way that corresponds exactly to its appearance when printed or displayed as a finished product.
This makes it easier for humans to design web pages, for example. However, the underlying code (HTML for web pages) is often more difficult to understand and change by a human.
WYSIWYG systems, especially for web pages, often lack features that are needed for advanced functionality.
For these reasons, professional web designers often create HTML manually rather than resort to WYSIWYG web page design systems.