An iFrame is basically a ‘window’ in your website whereby other HTML or files can be loaded in.
iFrames are inline frames that are used to load in other HTML documents to your website page.
They can also be used for things like YouTube embeds and displaying other HTML and code. There are better ways to do this sort of thing than by using iFrames, but they are common.
For example, if you wanted to embed a YouTube video to your site, you would click ’embed’ on the desired video, which would then generate a piece of code for you to copy and paste into your site. This code is an iFrame!
However, using iFrames should only be done from a reliable source. They can be a great method for hackers to access your site if they are just copied from any website.