My definition of a dystopia is a society in which the majority of the population is suffering due to environmental or social issues.
My favorite dystopian example is in the republic of Gilead in the Handmaids Tale. All elements of a dystopia are present in this show from environmental disaster to women losing all rights, to the general population being forced to live under unjust laws and censorship. A dystopia is basically a place that is opposite from a utopia which is the perfect paradise. In the handmaids tale the US has been taken over and forced fertile women to be raped and forced into sexual indentured servitude to force them to have children for the powerful men who rule the country. The birth rate has severely declined around the world and the government does not allow its people to use technology like TV or the internet to censor them. Punishment for breaking laws is usually violent. This is a dystopia because the majority of people are suffering.