Staking is used as a way to place amounts at risk against future performance. It is used in node operations, but stakes can be placed for multiple purposes. A given amount of ndau can only be staked once, and that amount is unspendable while staked. A single account can contain stakes for more than one purpose, as long as the total staked is not more than the balance of the account.
For more information about transaction types, see Transaction Fees.