Well I can honestly say that I've never heard of the term "memory strap." Maybe that's why others aren't responding?
Something more useful though was found on Google, searching for
"memory strap" definition.
Link
"Strap basically, is the Latency of the Motherboard, when different default CPU FSB's are used. Think of ram, and cas. well, motherboards have kinda the same thing."
Seems that it has to do with timings.