Can anyone explain what that means?
Because of network latency, two miners may publish a block roughly simultaneously and both blocks will be distributed through the network before they collide. Any given miner must pick one of the two blocks. The longest chain, in terms of proof-of-work performed, will always win. Ties are broken by whichever block a given node has seen first when mining.
If you have two competing blocks at the same count and one miner publishes a block after, it will lengthen only one of the two chains because it must pick one of the two blocks as its antecedent. Once this has propagated through the network, the preceding block that "lost" is an orphan.
Because of network latency, especially at 3 minutes per block, you can't prevent orphans from happening. Orphans are expected, and handled correctly -- by all Bitcoin and friends clients except CoinHunter's newest versions.
The reason why there is a 120 block confirmation on mined coins is because the generated coins in any orphan are invalid, and the client provides a lengthy wait to make sure that if there are two competing chains that forked several blocks in the past (due to, say, a broken network connection between two parts of the globe) they can be merged before the coins are spent. This is why sometimes a pool's solved block may suddenly show up as invalid 3 hours later -- it just took that long for it to lose.
CoinHunter broke the handling of orphan blocks. As a result you aren't just downloading a block chain, you're basically getting a block tree, and that's not how the system is meant to work...