A flash of unstyled content (FOUC) is an instance where a web page appears briefly with the browser's default styles prior to loading an external CSS stylesheet.
A Flash of Unstyled Content (FOUC) is a phenomenon which occurs when an issue with markup (HTML), styles (CSS), or scripts (JavaScript) causes the browser to briefly display the content of a Web page without any styles applied. This is generally undesirable since the page often appears quite different from intended.
If you are working on a Web page and you see content not displaying as it should for a brief period, followed by a correct display, this tag is appropriate for your question.