In cryptocurrencies, mining is the process of completing a new block of transactions and adding it to a blockchain. Miners are nodes in cryptocurrency networks that select transactions from the mempool, validate that the trasactions follow all protocol rules and include them in the created block.
Mining is typically a decentralized process. A successful valid block formation is a random event, the probability of which is proportional to the computing power of the miner's hardware. The reason why miners are motivated to commit their resources to mining is that they are rewarded by newly created cryptocurrency in each block they successfully create. Mining thus also constitutes the default way of decentralized cryptocurrency initial distribution.