Distributed consensus

How a cluster decides on one truth when some members might be lying, late, or dead.

Definition

A class of protocols that lets a group of machines agree on a single value or order of events even when some nodes crash or messages are delayed, dropped, or reordered.

Step 1

Predict first

In one or two sentences, what do you think this concept means? Wrong is fine; the small struggle is what makes the answer stick.