On Decimal all transfers are implemented by "validators" - these are the same members of the network as you, but they invested real money to server PCs to ensure their earnings from the network commissions. Their computers write down all your transfers and store this history for different purposes.
In order for the validator to have more power, to be able to process more transactions and get more commissions - it needs a "stake". Stake is the amount of money that the validator has on its balance. The more stake it has, the more transactions it processes, the more money it earns.
You can delegate (send) money to validator's account. In this case it will earn more and share part of the earnings with you.