> And how does this apply to logs? It's common for web servers by default to record urls visited and IP addresses. Would that be legal without explicit consent?
I'm not certain on the details, but in eg Norway that is already much in line with the GDPR ip addresses are considered personal data, and as such regulated. However, there are provisions for storing such information for auditing purposes (both security, technical and financial/invoicing) - but would likely require explicit consent. ("i accept"/"i will not use this service" - more of an informational confirmation - like signs stating a shop is under camera surveillance - and you could choose not to shop the (even if: good luck finding a shop w/o surveillance cameras)).
In general "personal data" is anything that can significantly help identify a single individual (time/place, ip, phone number/date, address, full name, email, etc).
Ed: regarding logging ips for auditing - there's usually a fixed time limit. It's longest afaik for financial purposes (and the data storage directive explicitly states/stated minimum duration - effectively being lobbied into a tool to go after amateur copyright infringement by forcing isps to keep records longer than before). But from a data protection viewpoint, you can't say/get consent for "we log for auditing" and then keep the data indefinitely . More like 6 or 12 months.