Eye tracking is a technology that allows you to see and record what a person is looking at, and for how long. One way it is used is to study web sites to see where people are looking on a web page, where they look first, second, etc. It’s a pretty interesting technology, one of the benefits being that you don’t have to rely on what people SAY they are looking at, but can collect the data directly. Like any technology, however, it’s not perfect, and one of the problems with eye tracking is that you can’t just give people a web site to look at and then assume that where they look is what they are “really interested” in.

https://www.blog.theteamw.com/2009/12/11/100-things-you-should-know-about-people-18-what-people-look-at-on-a-picture-or-screen-depends-on-what-you-say-to-them/