Description (From Recipaedia )
Wooden spikes penetrate flesh. The spiked planks can be placed on the floor, on the walls and on the ceiling. Touching them will cause injury. Trap pits are often lined with them. Spikes can be electrically controlled and will extend/retract on a rising edge of an electric signal.
Crafting
Crafting requires 3 sticks and 3 wooden slabs. You get 2 spiked planks.
Uses
Spiked planks are useful for trapping animals and fortifying your base.
Making a Trap
Find a heavily mob infested area and dig three or four blocks down then plant the spiked planks and climb out. Then cover your pit with grass trap and some markers so you don't fall in. Check on it daily and with luck, you'll be rewarded with food.
This kind of trap can spawn naturally. They are found in plains and snowy plains. You may walk into one, if you're not careful. These blend in with the environment, even hiding under snow! Animals may step into one pit, alerting you that the area may be covered in more pit traps.
Electrics
Spiked planks can be used with electrics. By sending a signal pulse to the planks, the spikes will either compress or contract. They can even be used in place of a normal door.