Accessibility is concerned with the issue of making sites usable to everyone. This refers to a specific form of usability aimed at catering for the needs of disabled users. As far as websites are concerned, the disability that is most relevant is visual impairment - partially sighted or completely blind users. You might think that it is impossible to create a website, a fundamentally visual medium, that can be used by blind people, but in fact it is quite possible - with a little planning and thought.
First, let's address a couple of myths.
Web sites are textual, not visual.
Of course, all web designers want their sites to look smart, and there's nothing wrong with that. However that doesn't mean that the graphics should get in the way of the content of the site. Almost all sites are created to transfer knowledge, from the site owner to the visitor. (That knowledge might enable them to buy something from the site, or just to know what you are about). The point is, the message is fundamentally a textual one, the graphics are just there to present your image to people who can see it.
The clever thing about text - as opposed to graphics - is that computers are now able to read it out to people who can't see it. Such software - 'screenreaders' - is widely available, and some operating systems even come with it as standard.
Graphic designers might lose heart at this stage, fearing that their skills are illegal and all sites should be text-only and black and white, but that is not the case at all. As long as graphics complement the textual message, and don't add meaning that is unavailable in the text, there is nothing wrong with a smart, visual site, with plenty of graphics.
Of course a bonus of the renewed emphasis on the text is that it will make you think harder about the words themselves. Clear, concise text is a pleasure for everyone.
There are lots of standards for website accessibility. You can choose from Section 508 in the USA, the Disability Discrimination Act in the UK, and industry-specific ones like SENDA for the education sector. Instead of going into the detail of these well-meaning documents, it is most productive to look at the fundamental principles - the underlying spirit behind them, and work out practical ways of making sites that adhere to those principles.
1) Links should be textual, not graphics.
This is an easy box to check, as neatComponents manages the generation of the standard navigation links between pages, and it always makes them using text. It does let you have graphics for the backgrounds, and you can style them however you like, but fundamentally they are text, and screenreaders can therefore read them out.
2) Graphics should have ALT text.
If you do use graphics in the body of the page, even if the content is just a pretty picture and incidental to the page, you should always have some alt text, describing in a few words what is in the picture. For visual users, the ALT text will appear as a 'tooltip' when the mouse is hovered over the image; screenreaders will say that it is an image, and read it out. This is a simple courtesy to the visitor, who would otherwise be left wondering whether the image was important or not.
3) Meaningful graphics should have a textual alternative.
A meaningful graphic - for example a pie chart - should have a textual table next to it containing the same information. This is also a classic example of solutions for the visually impaired which are also useful to everyone.
4) Uploaded documents should be accessible too.
Don't forget uploaded documents. A PDF file may look good, but it may not be as accessible as a Word document. Consider uploading both formats. And the guidelines about meaningful graphics also apply in those documents.
Putting it into practise
This has only scratched the surface of the accessibility topic, but it has covered the most important parts. If you can, get hold of a screenreader, and listen to your site; or, even better, talk with someone who is visually impaired, and hear first-hand their experiences of trying to browse the web. More than anything else that will inspire you to create an accessible site for the right reasons - not just to check the accessibility box in the regulations.