What is the 'selected parent' in Kaspa's blockDAG?

The selected parent is the one block, chosen from among all of a block's parents, that carries the highest accumulated blue work. Kaspa's blockDAG allows multiple blocks to exist in parallel, so any new block can reference several prior blocks as parents at once. To keep the entire network in agreement about transaction ordering, the protocol designates the parent with the most blue work as the selected parent; chaining these selections together forms a main chain backbone that runs through the otherwise branching graph while still acknowledging the other parent relationships. This matters to a beginner because it shows how Kaspa maintains a consistent ledger without discarding the parallel blocks that a traditional blockchain would simply throw away.