Stake

In many systems not all validators will have the same "weight" in the consensus protocol. Thus, the interest is not in the one-third or two-thirds of the validators but in those proportions of the total voting power which may not be uniformly distributed across individual validators.

Since Tendermint can replicate arbitrary applications, it is possible to define a currency and denominate the voting power in that currency. When voting power is denominated in a native currency the system is often referred to as Proof-of-Stake.

Validators can be forced by the logic in the application to "bond" their currency holdings in a security deposit that can be destroyed if they're found to misbehave in the consensus protocol. This adds an economic element to the security of the protocol therefore allowing one to quantify the cost of violating the assumption that less than one-third of voting power is Byzantine. The E Money Network is designed to use this Proof-of-Stake mechanism across an array of cryptocurrencies implemented as ABCI applications.

The following diagram is what Tendermint is in a (technical) nutshell.