I’ve had LinkedIn described to me by various people. If they are over the age of 30, they say something like “It’s a social network for professionals. It’s for professional networking. You should get a profile, It’s good for your career, it’s not what you know but WHO you know.” If they are under the age of 30, they say something like “It’s basically an online resume, a lot of jobs you can apply for using your LinkedIn profile.”
Although, in MY experience, LinkedIn is pretty much just a spamming annoyance.
Something you should know about LinkedIn: If you have it, and you have me as a contact through facebook or email or ANYTHING, i’ve probably received at least three notifications saying “(person) is waiting for you to respond to their invitation to join LinkedIn”… a simple inbox search shows that I have 47 invitations/reminders to join this site… so it’s not quite 2508, but i mean, it feels like it.