Here is what I know, so far - please fill in the missing ones - thanks:
Layer 7 - Layer 6 - Layer 5 - Message? (not sure) Layer 4 - Segment (TCP) Layer 3 - Packet or Datagram (IP) Layer 2 - Frame (Frame Relay) or Cell (ATM) Layer 1 - Frame (T-carrier 193-bit frames for example)
Google is your friend.
There's also the local library.
Everything _is_ on Google :-)
This just goes to show that formulating the right question is a greater art than finding the answer :-)
And to the poster: No, there is no real reason why they choose 7 for the number of layers. It took them 7 years to get there. That's the closest to an answer I have ever seen. They could have choosen almost any number.
The forte of OSI is, that they showed the networking community that it is smart to slice the problem. And that it works best if everyone agrees on the boundries between the different functions.
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