An Orphan block is what is made when a person mining by either Proof of Work/Stake finds a block on the wrong chain, leaving the block rejected by the official blockchain.
Proof of Stake
When an orphan block occurs via proof of stake mining, it is because another block of HoboNickels staked at the same time and the blockchain accepted the other block's stake rather than your stake. The PoS transaction in the QT client will show 0 confirmations, and only exists in your own client and is not recorded to the blockchain. If you get an orphan, simply keep your wallet as is and your HBN block will remain in the pool of blocks competing for stake, you did not lose any coin age that has accumulated. Furthermore the way HoboNickels are designed, the higher the coin age the more staking bonus you will get. So in the case of an orphaned PoS block, you will not "lose" anything because you will be compensated for the extra time the block took to mature.
Checking Coin Age
Often times when a PoS orphan is created, the user will be concerned that there aged HoboNickels block will have to start the aging process over and that they have spent the last ten days of aging for no reason. To double check that the block is still mature simply use the coin control feature in the wallet client. Go to the send coins area and select the input button (if you can't find this refer to the Coin Control page). Select List Mode and you will see all of the blocks held by the wallet. On the right side you will see confirmations - this is how you will determine the age of your coins. 28,800 confirmations is about 10 days (30 second average confirmation speed).
Proof of Work
Orphans can occur during proof of work mining when a worker is not properly synced to the correct chain. For instance, let's say there are three miners, Alice, Bob, and Charlie all mining Examplecoin when it is first being released. Bob gets lucky and finds the first block of the chain, which then rewards him with 5 Example coins. Wanting to make more coins, Bob continues to mine coins on the second block, while at the same time, telling Charlie to start working on the second block with him. Sadly, Alice does not hear that block 1 has been found, and is still working on the original block. After some time she solves the first block, however, since the block has already been solved by Bob, no Examplecoins are paid out to Alice, and her efforts were in vain. The only way to safe-guard yourself from getting orphans is to maintain a steady internet connection so that you can "hear" whenever a block is found so that you can move on to the next.