Ethos is the spirit of a time or society. It’s the set of beliefs a community lives by. Free spirits might live by the ethos of "anything goes." Zombies might live by the ethos “eat more brains.”
The noun ethos refers to the particular rules and values that organize people, although the ethos can vary from group to group. For example, in some cultures individual rights might be highly valued, while in others the good of the community as a whole might be considered more important. The Greek root word ethos is related to “ethics” and refers to moral character. In rhetoric, an appeal to ethos means that a speaker attempts to persuade the audience that she is authoritative and credible.