mmm kay
They are all a continuum, but generally you can only get two at a time.
Consistency means that whatever data you have is never stale. It is never wrong. You relax this by saying it is never more than one version out of date or it is never more than 2 minutes old.
Availability means you always have data at your fingertips. You never have to wait long for it. Fetches return immediately with what you expect them to. The data may or may not be current. You relax this by allowing things like "Data is locked by other user - please come back tomorrow" states.
Reliability or Scalability implies that the system is always up - it can scale with just the addition of hardware and is capable of withstanding component/peer failure. Relaxing this means using something like a central lock server to manage data consistency introduces a single point of failure that will take down your system. Doing this will cause to to relax availability.
Here's a great talk about this stuff by Werner Vogels. [link|http://www.itconversations.com/shows/detail459.html|http://www.itconvers...ws/detail459.html]
