A light client, also called a thin client, only downloads all the block headers. They are trusting the full node, since they can’t check transactions themselves using only the block headers. The light client can see that the transaction has been accepted into the network, and they can tell how many blocks deep a transaction is. A light client’s greatest asset is time. The longer the node waits, the deeper it is buried in the chain and the more unlikely it is that a longer chain will emerge.