What do they mean by a reference board?

"Reference board" refers to the card engineered by the chip manufacturer.

When a company like nVidia makes a new chip (i.e. GF3) they have a company make a board for that chip. Since nVidia does not produce boards, only chips, they make the board with little to no frills and a basic layout that they will gaurantee to run stable to the card manufacturer like Hercules and Elsa.

When a reviewer says something like: The board used the reference desgn, that means that the card manufacturer followed the design of the chip maker placing the chip, memory and other components in the same place as the reference design, with no serious deviation to be seen.

There are a few examples of card manufacturers chucking the reference design for their own but they are few and far between.

Hope this clears it up for you.

Check out my rig:
<A HREF="http://www.anandtech.com/mysystemrig.html?id=3737" target="_new">http://www.anandtech.com/mysystemrig.html?id=3737</A>