What is the mergeset in GHOSTDAG?

The mergeset is the collection of blocks that the GHOSTDAG protocol evaluates to assign each block a color and determine which ones contribute to network consensus. In Kaspa's blockDAG, multiple miners can produce blocks at the same time, so the network needs a way to decide which parallel blocks actually drive the shared transaction history forward. GHOSTDAG does this by processing each block's mergeset and coloring the result: blocks colored "blue" contribute to consensus, while blocks colored "red" are valid and accepted by the network but do not advance it. This coloring system is what lets Kaspa handle parallel blocks without falling into disagreement — without it, there would be no way for every node to agree on a single history.