Creeper Head is an item added by vanilla Minecraft. It is the head of a Creeper that sometimes drops when killed by the player. The Decapitate enchantment increases this chance up to 100%.
This mob head, like all others, can be worn by the Player when put in the Helmet slot. The Creeper Head is purely aesthetic; your field of view is unaffected, provides no Armor points and has no Durability counter.