The detonation was expected in June, a delay from the previously planned December 2021 date. This time, developers decided to push back the difficulty bomb after discussing numerous bugs they discovered when they tested the software on the freshly merged Ropsten.
According to core developer Tim Beiko, the two months delay was sat in order to “be sure that we sanity check all the numbers before selecting an exact delay and deployment time.” Beiko also quoted other Ethereum dev Marius Van Der Vijden, saying that the delay won’t slow down the team’s work on the Merge, as it’s just “‘a five line change’ for clients and is easy to implement.”
The difficulty bomb is a special code meant to disincentivize Ethereum miners after the transition to the proof-of-stake consensus. It exponentially increases mining difficulty every 100,000 blocks, drastically reducing profitability until it becomes impossible to validate a block. According to Ethereum’s client Nethermind, the difficulty bomb acts as a defense against attackers that fork the network.