What Is a 51% Attack and How Does PoW Prevent It?

A 51% attack occurs if a single entity or group controls more than half (51%) of the network's total hashing power. This dominance would allow them to potentially reverse transactions, double-spend coins, or prevent new transactions from being confirmed.

Proof-of-Work prevents this by making it extremely costly and computationally difficult to acquire and maintain such a large amount of hashing power. The economic incentive favors honest mining.