In 2000, the sports card company Topps had an idea: sell cards individually with limited print runs and make them available online as "virtual cards" before they even get printed.  After they are sold and the cards are distributed to buyers, never print that card again.  If the card didn't sell out, whatever quantity was bought would be the final print run.

Each week (and lasting 7 days), etopps offers 5-7 cards with IPOs set at a certain price and has a print run (PR) limit for each card.  Those who are registered members of etopps (which requires a credit card but there is no registration fee or obligation to buy), can order as many as they want of a particular card (even the whole print run!) but may not get all that they requested to buy. 

For example, after the week-long availability of the 2005 David Wright card, etopps notified the members via email how many they were allocated. 

If it was considered a "hard" sell-out, members may get just one of that card.  If it was a "soft" sell-out, they may get up to the quantity they had ordered of that card. 

Usually, if a card does not sell out members will receive the entire quantity that they had ordered for that card.

Once that David Wright card was allocated, the secondary market for the card begins, which is usually ebay.

 Those who want to make a quick buck (aka "flippers") sell them as soon as they are allocated in hopes of selling the card at a higher price than the IPO price. 

An alternative to ebay is the cardtarget website where you can place a buy order on the cardtarget market.

As on online card, it is held in one's online portfolio which can be accessed on the etopps website as well as manually on the cardtarget website.  These cards can be traded on the etopps website, bought or sold on ebay or cardtarget and, more recently, in fantasy sports on the etopps website. 

Going back to the example of David Wright, after a certain amount of time, this David Wright card became available to be shipped and have the status of being "in hand." When this happens, the Wright card can be removed from one's on-line portfolio and be shipped to one's home.

Let's say the print run for the David Wright card is 1,000 (just an even number, not the actual total print run).  Having one of these cards shipped to one's home implies it is removed from on-line circulation and the total print run on-line is now 999 and the in-hand print run availability (if there is only one taken out-of-port) is now 1 (if you are the only person who has had this card shipped).  Once that card is taken out-of-port, it cannot be switched back to in-port so once it's taken out, it's out.