When you visit a website your web browser saves information to your computer to enable web pages to perform quicker.
When this data is saved it is called browser cache. Normally this is a positive thing as it ensures that the browser does not need to download the same static resources over and over again.
For example, header names do not often change within a webpage so it is beneficial for the header names to be stored as browser cache to prevent this data needing to be loaded every time you access this page.
However, sometimes browser cache can prevent you from seeing a change that has been made to a page as the data is being loaded from your local storage instead of directly from the webpage. In this instance, you would need to clear your browser cache.