"Negative ads" refer to a type of advertisement that focuses on criticizing or attacking someone or something, rather than emphasizing the positive aspects. Full definition
This election season seems to feature more than the usual amount of negative ads, with television spots painting opponents in a dark light. (wxxinews.org)
The union spent far more on negative ads against her than on behalf of three candidates it endorsed. (articles.latimes.com)
With speculation the outcome could decide the majority in the state senate, outside groups spent millions on negative ads. (nystateofpolitics.com)