Tim O’Reilly, during his talk for TED:

He gives a metaphoric example of people wearing name tags in the real world and semantic description of these people on the semantic web, assuming that they are identified by an RFID tag.

we don’t wear name tags all the time [to get identified]
[…]
if we meet again, i will not recognize you because you’re wearing a name tag, i will recognize you because “oh yeah, i’ve seen you before!”
[…]
=> our machines are becoming like that

He uses this metaphor to show that the actual “Semantic Web” is filled progressively by learning from the “wisdom of crowds”:

Semantic web /RFID is things wearing name tags, and web 2.0 is learning to recognize them. So many things are continuously getting better at recognizing things by accumulating context, bit by bit.