Heaviest Chain Rule

From this post:

"The longest chain rule & heaviest chain rule: When multiple chains exist, for instance due to attacks attempting to break ledger’s immutability, the chain with the longest string of blocks was originally selected as ‘the true version’ in Bitcoin. Since blocks can only be created through PoW, the longest version was considered to be the most difficult to create and could thus be the only ‘true version’ of the ledger. More recently, this was adjusted to the ‘heaviest chain rule’, where the chain that got hashed the most is selected, making this assumption more explicit."