What is the definition of aggregate user data?

I've been trying to understand some of these online privacy agreements. Most of seem to be on the up and up, except for one term that scares me, "aggregate user data". It sounds like something a politician would say. Extremely vague. In the case of online friends websites, the amount of information entrusted to them increases the scope of "aggregate user data". I did a search and found it to be a very standard term used in most privacy agreements. Much of the time I've found assertions that "we do not link aggregate user data to personally identifiable information." The freinds website does not make that claim. What does it all mean?What is the definition of aggregate user data?
Those are elements assembled into a logical format to facilitate comparisons OR to elicit evidence of patterns. Those elements by themselves cannot identify no one in particular but when you link them to others it is possible to identify some people based on their profile. In example you link certain people with certain phrases or way of speaking or writing. Those are element you can put together to find who is the writer or the speaker.