There has been some confusion lately with some sellers trying to sell their cards with incorrect information.  For instance, one seller was trying to sell a "Secret Rare" card, to which in the picture shows an "Ultimate Rare" card.  I'm going to give you buyers and sellers the 101 on Yugioh Rarity Types.

Normal: Plain and simple, no special writing, no holographic picture, just a card. 

Silver Letter Rare: The only difference is that the letters of the card name is done in Silver.

Super Rare: The card name is not changed, but the picture is holographic.

Ultra Rare: The name of the card is in Gold Lettering, and the picture is holographic.

Secret Rare: The lettering is bright whitish/silver, and the picture is holographic and with diagonal lines.

Ultimate Rare: The lettering on the card is Gold, just like an Ultra Rare.  However, the holographic picture, and the attribute symbol on the upper right are darkened.  The holographic picture that is darkened have some unique designs on it, not all ultimate rare cards have the same design.

Parallel Rare/Ultra Rare Parallel: The new idea from the Japanese card game, gives you the same Gold lettering card, like an Ultra Rare.  However, the card has a glossy holo finish, to which you think the picture is holographic, but its a card sticker.  When you turn it in a certain direction, you can see squares.

Ghost Rare: The newest and most valuable card to get.  The lettering is the same as a Secret Rare, but the picture is very of a dark variety.  Its not an ultimate rare, but a parallel version of the picture, to which if you turn the card at a different angle, you can see the picture better.  Very difficult for sellers to photographic.

Thats is all of the Varieties of cards so far in the Yugioh World.  Just remember to always check up on the cards name and the rarities that they come in.  Remember, there are going to be copies of your favorite cards.  The key for higher value is rarity, and sometimes the higher price is not always holographic (Ex: DP04 Cyber Dragon Silver Letter Rare)