Like its Mirrodin predecessor, Sword of Kaldra, it is a piece of Legendary equipment that grants some mighty abilities to the creature that wields it.
But unlike the Sword, the Shield of Kaldra has a mysterious name sneaked into its rules text:
Equipment named Sword of Kaldra, Shield of Kaldra, and Helm of Kaldra are indestructible.
Is it just a flavorful addition, in case such a Helm is printed later? Could some obscure combination of existing cards create a piece of equipment by that name, right now? Could the Helm be a new, previously unknown card, to be printed at some future date (and if so, what abilities would it grant)?
And who is this "Kaldra," who owns, or owned, such powerful possessions?
We at Magicthegathering.com don't intend to answer these questions at this time. But who knows, perhaps you'll learn more about this Kaldra person -- or entity? -- on this site sometime soon.