Canonical
Once confirmed a block becomes canonical and is added to the chain of historical blocks in the blockchain. Non-canonical blocks may be valid, but discarded in favor of the canonical block.
This is relatively common for proof of work chains. Two miners with separate candidate blocks often find the valid block hash around the same time. Causing the chain to temporarily split with different nodes supporting different candidate blocks.
Eventually the nodes arrive at a consensus on which candidate block to confirm and add to the blockchain’s history as the canonical block. Over the other proposed candidate blocks which are subsequently discarded.