What is an orphaned block in a traditional blockchain?

An orphaned block is a valid block that gets discarded because another block at the same height was chosen by the network first. In a traditional blockchain, miners around the world compete simultaneously, so it is possible for two miners to produce valid blocks at the same moment. The network can only accept one, so the other is thrown out along with all the computational work that created it. For a beginner, orphaning matters because it represents wasted effort and is the main reason traditional blockchains have limited throughput — only one block can be accepted at each level of the chain.