Shorewood Husk can be found right under the Shorewood Leaves of Shorewood-trees that grow on Ocean Shores, as well as around oases or sandy river-banks in Dunes or in Savannah-biomes.
Shorewood Husk can be placed as solid blocks and even used for building. It is rather rare, and currently it's not a necessary material for any crafting-recipe.
2 blocks of Shorewood Husk each can be used as Fuel and are just as effective as any kind of Wood, and flammable as well.
Shorewood Husks can also be corrupted, for example by Corrupt Bombs. They will turn into Corrupted Wood by that, and when purified again, they will become Cragwood.
However Shorewood Husks are not really the same as Wood, and so they cannot be made into Slabs nor Rods in the Processor.