On the Smashing Magazine site there's a new article talking about coding style matters with developing projects with multiple people (or even possible contributors in the future) involved.
Coding style is how your code looks, plain and simple. And by "your," I actually mean you, the person who is reading this article. Coding style is extremely personal and everyone has their own preferred style. You can discover your own personal style by looking back over code that you've written when you didn't have a style guide to adhere to. Everyone has their own style because of the way they learned to code.
They talk about how everyone has their own personal "style" to their code and how, when working with a team, everyone needs to communicate and make sure their styles match. They also make a few recommendations for your code like leaving "clues" (comments) and making errors easier to spot. There's also a few links to tools that can help keep your code standardized including CSS Lint and the Eclipse code formatter. PHP, of course, has its own - PHP_CodeSniffer with its own rules.