A plant cultivar bred or selected to genetically resist specific pests or diseases, often indicated by letter codes (like "PM" for powdery mildew resistance).
Breeders select and breed plants that are genetically resistant to specific pests or diseases. A powdery mildew-resistant (PM) variety won't develop that disease even in humid conditions. Resistance is variety-specific and sometimes site-specific; a variety resistant to one pest might be susceptible to another. Choosing resistant varieties prevents problems before they start.
Choosing resistant varieties is the simplest, most effective pest management strategy. Prevention beats cure every time.