Ethos is a Greek word meaning "character" that is used to describe the guiding beliefs or ideals that characterise a community, nation, or ideology. I've never heard this word from native speakers.

'Ethos' is a academic term. We can persuade people by three kinds of methods: ethos, pathos and logos. Here are examples. "As a doctor, I am qualified to tell you that this course of treatment will likely generate the best results."(Appeals to Ethos-to ethics.) "If we don’t move soon, we’re all going to die! Can’t you see how dangerous it would be to stay?"(Appeals to Pathos-to emotion.) "In 25 years of driving the same route, I haven’t seen a single deer."(Appeals to Logos-to logic.) (Source: http://examples.yourdictionary.com)