DNA is just PSA's name for their autograph authentication service. For a fee you can send a piece of autographed memorabilia to PSA and they will render an opinion as to the signature's authenticity. If their opinion is that it is authentic the item is considered PSA/DNA certified. Larger and expensive items will likely come with a LOA from PSA, photographs usually come with a applied sticker, and cuts-index cards-and trading cards are usually encapsulated in their slab.
