I called them ledger boards; Jeff Miller just calls them cleats.
That's a very useful reference. Even the Amazon "Peek Inside" provides plenty of information for someone with as much experience as most of us here, to choose a construction method and build a soundly joined bed. I think I may even have a copy of the book somewhere.
Instead of ordering it directly from Amazon, a book seller listing on abebooks.com currently offers two used copies for $4 each with free shipping.