GUI in backend to define constants without any programming knowledge. Every file in your theme has access to your constant.
If you have a contstant named MY_TWITTER_URL ... You can use something like this in your PHP template file:
<a href="<?php echo MY_TWITTER_URL;?>">Twitter</a>
Or install a PHP in post plugin and use
http://pluginsupport.mijnpress.nl/ or drop me a tweet to notify me of your support topic over here.
I always check my tweets, so mention my name with @ramonfincken and your problem.