Web developers and designers and even your average internet user would understand exactly what a 404 error page is.
Simply put, it is a page that shows up when a user tries to browse the page that no longer exists or if the link is broken or perhaps the content had been moved. In some cases the link never existed and probably never will. Usually the 404 pages are dull and cause users who reach that page to get annoyed but that does not have to be the case. It is up to you how you design it and most of the popular websites have a very creatively designed 404 error page so that their audience will not be irritated by landing there.
Bigger companies would design the 404 error page from a very functional point of view as well. Why, you ask? Well, quite simply, the page you are looking for is obviously not there so the designer and the company would make sure that once you land there, you get to find what you are looking for easily and perhaps provide a way for you to navigate out of there as well. So for your inspiration, we have come up with some intuitive and creative 404 error pages. We hope they give you some ideas.