RAM question (2Rx8 vs. 2Rx16)

Ok this isn't really a burning issue but it has been driving me crazy trying to find out as general computer info. I have 2 new laptops and I was going to swap some memory (Take a 2GB stick from one and switch with a 1GB in another to change the amount in each one). When I opened them up the sticks in one system both said 2rx16 on them and in the other system both sticks said 2rx8 on them. They are both DDR2 RAM @ 667Mhz. I did the switch and both systems work fine with the switch but it is bothering me I can't figure out the difference.

A google search gave me an apple forum post as the first hit but all it said was this

2Rx16 (two ranks, of x16 bit devices)

2Rx8 (two ranks, of x8 bit devices).

This explains in a much more in depth way.
The link in there takes me to some site but it doesn't make any sense.

Does anyone actually know what it means? I am thinking it just means the number of modules on the RAM sticks? Thanks for the help.

Message was edited by: Randy Fast