Seek is a keyword ability in Shadow Era, first introduced in Lost Lands.
You can learn about the Seek mechanism code in the Seek discussion article.

This keyword ability allows the player to search their deck for a certain type of card (e.g. an ally of a particular alignment) and add that card to their hand after revealing it to the opponents.

• A seeked card must be revealed only if and only when it doesn’t have the `(PlayFaceDown())` function attached to it, as is the case for Traps.
• Players will shuffle their deck after seeking a card.
  
• Players can not seek if their hand is full.
  
• When a card is searched out with this ability, it is also revealed to all players, placed in the player's hand, and the deck is shuffled afterwards.
  

This ability is intended to allow players to gain increased reliability of getting the cards they want into their hand when they need them.

There are some situations where players have one ally with Seek Item, then this item with Seek Location and then Location with Seek ally.
-> Those cards in one deck (12 cards) will make the Seek circle so you will be able to find everything in your entire deck! It will not matter much what you will draw first, they can find each other. With 12 cards in deck its almost sure you have one in opening hand... (source)

Discussion in the forum about seek:

• The power of seek