A validator is a piece of software that runs on a computer or virtual machine that validates the SafeCoin ledger (keeps it consistent with other validators) and produces new blocks on the SafeCoin blockchain. This is essentially a piece of the backbone of the SafeCoin network that you can run on your own computer.
You can run a validator in one of two configurations. A full history node keeping 2TB (Annually) of the ledger on your computer or a pruned node keeping only 20GB of the ledger. The only difference (as of this writing) is how much drive space you want to allocate to the ledger.
Running a validator is an important part of being a community-based decentralized network and will help to ensure smooth network operation. In addition to this, if your validator creates a block (as the leader) it will be rewarded, and that doesn’t need to be shared with those that delegate SAFE to your validator. The chances of your validator minting a block are random but with probability based on their delegated stake amount and reliability.