Blockchain, longest chain and reorg’s

The "longest" chain refers to the blockchain which took the most energy and accumulated work to build, hence it's also referred to as the "strongest" chain.

The longest chain refers to the blockchain which individual nodes accept as the valid version of the blockchain, allowing said nodes to agree on the same blockchain and thus, the same transaction history.

Occasionally there’s a short-lived uncertainty between nodes about the longest chain, which happens when two miners mine and broadcast a new block at (almost) the same time.

Due to the propagation speed of blocks across the Bitcoin network, different parts of the network will receive one of either two blocks, leading to some nodes following Chain A, and others Chain B.

Once the next block is mined, broadcast and validated by the network, it will be added to the end of either chain A or chain B, creating a new longest chain, leading to the respective nodes following the other chain to perform a chain reorganization in order to catch up.

A chain reorganization refers to the process of adopting the new longest chain.

Once the chain reorganization has been finished, block(s) on the new longest chain will be activated, and block(s) that were part of the other chain will be deactivated, leading to them no longer being a part of the transaction history of the longest chain and thus, the blockchain.

The deactivated block(s) from the other chain are referred to as (a) "stale block(s)", which refers to block(s) that are no longer part of the longest chain. Transactions that were contained within the stale block(s) but not in the longest chain, will be recycled into a node’s mempool, and propagated across the Bitcoin network once more for a chance to be mined in a future block.

I'll have it expanded, let me know what to correct / add!