The ethereum main net uses, untill now, the Proof of work as a mechanism of getting the blocks(transactions inside) agreed upon and added to the blockchain.
The proof of work requires the nodes in the network to do some work in order to prove their "will to be part of the network". working and succeeding in completing the task is rewarded by currency to the winners, that is mining (basically working hard to find gold/coins).
Voter nodes can be anything, i have no idea what a voter is in the current ethereum implementation. In other blockchain implementation like quorum, voter nodes can have multiple meanings : voters can vote to add or not new validators in a proof of authority mechanism.
validation is the fact of making sure all the participants(fully working not light nodes) agree that a certain node in the network can create the next block and recieve the reward. in PoW the Validation is when a request of validation of the results of the work of a certain node is broadcated to the network in order to see that the results are genuin.
Honest node :
An honest node is basically a fully working node with no intentions of creating false transactions or malicious blocks. It is a node that follows rules.
Fraud node :
a node that doesn't follow the basic rules, a node that sends false transactions, a node that trys to attack the network, ...