Crypto glossary
Solo mining
Solo mining means trying to find blocks alone instead of joining a pool: the miner keeps the whole reward when it wins, but wins very rarely.
A solo miner points its hardware at its own node and builds its own block templates. If it finds a valid block, it collects the full subsidy plus fees. The probability of that happening on each block equals its share of total network hashrate, so a miner with a tiny fraction of the network may wait years, or forever, for a single success.
Most miners join pools precisely to avoid that variance. Solo mining survives as a lottery for hobbyists running small devices, often through solo pools that handle the infrastructure for a fee while still paying the full block to whoever finds it. Every so often a home miner with a few terahashes wins a block, which makes headlines. Large industrial miners sometimes mine solo because their hashrate is big enough to find blocks regularly.
Solo mining also matters for decentralisation, since each solo miner chooses which transactions go into its blocks rather than relying on a pool operator. The financial reality, though, is that expected income is the same as in a pool, only far more irregular, and electricity bills arrive every month.
Example
A hobbyist running a small 1 TH/s device has, at current network hashrate, odds of finding a block on any given day comparable to a lottery ticket, but if it happens they receive over 3 BTC.