Definition
Block find probability can be calculated as: P(per block) = miner_hashrate / network_hashrate. For time periods: P(per day) = 1 – (1 – P(per block))^144, since approximately 144 blocks are mined per day.
For a Bitaxe at 500 GH/s against a 600 EH/s network, the probability of finding at least one block per day is roughly 0.000083% (about 1 in 1.2 million). Expected time to find a block: approximately 3,300 years. Despite these odds, blocks have been found by small solo miners, proving that probability is not impossibility.
In Simple Terms
The odds of your miner finding a block based on your share of network hashrate. Low for small miners but never zero.
The statistical likelihood of a miner finding a block in a given time period, based on their hashrate relative to the total network hashrate.