Halving is a process that runs automatically which reduces the bitcoins earned by creating a block by half. This process was created to encourage mining through proof of work. This in order to establish that every X number of blocks, the emission must be reduced by half.
This was born since the amount of bitcoins that may exist is finite and it is established in the Bitcoin software that the maximum is 21 million units. No more no less.
However, the number of bitcoins that are released is not always the same, in the software it is established that every certain number of blocks is reduced by half. This automated process is called halving and serves to establish a certain time until the end of the issuance of cryptocurrencies with the aim of pursuing a deflationary model, or what is the same, that the value rises gradually.