A wood block is a block that appeared in SMB3. There were three kinds; one that acted like a normal cement block, one that would push you back when you walked into it, and one which did the same as the second, but spawned a Mushroom, Fire Flower or Raccoon Leaf( the second was usually spawned by nudging the third). The first kind of wood block was common, first appearing in 1-1, the third occasional (first seen in 1-3) but the second alone much rarer.
In SMW, there are two unused blocks that use the Turn block graphic that work very much the same as the Wood block, blocks 12A (or 39 in the "Extended objects" selection) and 12B (B is spawned by nudging A, like the block above). 12A spawns a Feather when Nudged, while 12B spawns nothing. However, possibly as a roll-over from SMB3, the two block's Bounce sprites use the P-switch graphic. this can be changed to the Turn block bounce graphic by Hex editing x113F4 from 42 to 40.
Also,block 140, an unused, unbreakable block that uses turn block graphics, is speculated to be the first kind of Wood Block, as it uses the same graphics as the two unused Wood blocks, the turn block and Icey turn block, and one other block.