An orphaned block is a block where the parent block does not exist or is unknown.
What Is an Orphaned Block?
An orphaned block is a block where the parent block does not exist or is unknown. These types of orphaned blocks were formed in older versions of the Bitcoin core software, where the network nodes had the ability to receive blocks even despite the lack of data about their ancestor. Now, since the release of what is known as the Bitcoin Core v.0.10 in early 2015, Bitcoin orphaned blocks are an impossibility.
The term orphaned block is still used in the world of cryptocurrencies and it refers to valid minted blocks that have been discarded. These blocks can be called stale blocks or extinct blocks; however, because the client denotes their block rewards as orphaned, many people refer to them as orphaned blocks instead. Despite them having a known parent block, people still refer to them as orphaned blocks rather than stale blocks, but you should know the difference between them nonetheless.
An orphaned block is generated when two different miners relay their valid blocks at almost the exact same time, which causes the network to split into two competing versions of the blockchain until one of the blocks ends up being discarded. The longest chain prevails while the other is abandoned as a general rule. While both blocks are verified and valid in this case, only one of them can be attached to the main chain.
Now, given the fact that miners are constantly generating new blocks around the clock, certain blocks can be broadcasted onto the network simultaneously. Given the fact that the network itself is distributed, the transmission of this information between nodes can take quite a long time. As a result of this, a possibility exists that a group of nodes will end up choosing to validate one block, while another group will choose to validate another. Later, a consensus is reached by nodes determining which block will be accepted. This is what would cause one of the blocks to end up being orphaned.