Pre-mining is a process in which the development team mines a certain amount of digital currency (tokens) for themselves before the official launch of a new project. Coins are generated by a software algorithm rather than being mined in the usual way.
In open pre-mining, coins are used to pay for listing on crypto exchanges, various commissions, fees, ICOs (initial coin offerings to reward early investors), and incentives for the developers themselves. Everything is announced officially, indicating the number of tokens created and what they will be spent on.
In addition, there are crypto projects where all tokens can be pre-mined at once. Such platforms operate on the PoS consensus algorithm: coins are mined immediately at 100% and released to a wide audience. However, there is also a hidden pre-mining, when the distribution of the created coins is done in secret from the community itself, often for the purpose of personal enrichment.