Accessibility is a broad concept but in the context of the web buzzword it’s about making your website inclusive for as many visitors as possible.
The web has a broad range of users such as those hard of sight or hearing and accessibility is perhaps a larger issue than most website owners assume. There are guidelines (known as WCAG) that standardise what is best practice in terms of accessibility and most businesses should be aiming for a double A standard (AA) according to those ratings.
As well as being beneficial for disabled users, many of the WCAG recommendations make your website more usable for everybody. It wasn’t long ago that many websites utilised tiny fonts and low contrast grey text on grey backgrounds making the web virtually unreadable for anyone who wasn’t 20-something with perfect vision. It’s since been shown that larger fonts make for an easier and more relaxed experience for everybody. There are many other accessibility touches such as text tags for images and reducing the amount of text in images which have benefits for search engine optimisation. It’s certainly not something to be ignored!