When websites are created we can get caught up in how we see it. But what about if we have some visual impairment and do not see the world as you do?
Fonts can be difficult or even just too small. I am getting older (still very young) and was told this year I had to start using reading glasses. Some websites use font sizes that are too small for me to comfortably read.
I could increase the zoom of the browser but that would increase the size of all websites until I changed the zoom again.
Accessibility features within a website can add options for the person viewing your website. These include changing the font size, changing the font, making the site grey scale or black and white only.
For WordPress there are many plugins that do this for you and by using them you can make your site easier for everyone to use.