Overclocking is a method of squeezing more hashing power out of a mining machine.
As mining difficulty increases and hashprice drops, miners will sometimes resort to overclocking their machines to boost revenues. These changes can be made by increasing the operating frequency of the ASIC’s chips in the miner’s firmware. But this performance boost comes with efficiency tradeoffs.
An overclocked ASIC will simply consume more power to generate more hashes than it otherwise would at standard settings. Higher hashing frequency increases the probability that miners will solve a new block, but this process sacrifices efficiency for greater total hash outputs. Overclocking can also reduce the lifetime of a machine.
Older generation machines with de facto lower efficiency, however, can be prime candidates for overclocking. Overclocked older models can help miners eke more utility from before discarding their ASICs.