That stands for Automated Content Access Protocol. It’s fiercely deconstructed by Andy Oram in An editor critiques the publishing industry's Automated Content Access Protocol. I’m really unconvinced, first that this is really needed, or second that there’s any good reason for the people running the big crawlers to adopt it. They say ACAP is set to become the universal permissions protocol on the Internet but you know, we already have one, you can access-control anything you want. In the developed world, we have a perfectly competent legal system that allows publishers to hold Web sites accountable for how they use the content they fetch. If the people advancing this included anyone who actually liked the Web, it might be more convincing.