CADR stands for Clean Air Delivery Rate, which is an indicator of the effectiveness of an air purifier in removing pollutants from the air. It is a standardized measure developed by the Association of Home Appliance Manufacturers (AHAM) and is used to compare the performance of different air purifiers.

CADR measures the volume of air that an air purifier can clean in a specific amount of time, typically measured in cubic feet per minute (CFM). The three main types of pollutants that CADR measures are tobacco smoke, pollen, and dust. Each pollutant is given a separate CADR rating, and the higher the CADR rating, the more effective the air purifier is at removing that pollutant from the air.

For example, if an air purifier has a CADR rating of 200 for tobacco smoke, it means that it can remove 200 cubic feet of tobacco smoke per minute from the air. A higher CADR rating indicates that the air purifier is more effective at removing pollutants from the air.

It should be note that CADR ratings only measure the effectiveness of an air purifier in removing pollutants from the air without considering other factors such as noise level, energy efficiency, or the type of filter used. When choosing an air purifier, it's important to consider all of these factors to ensure that you choose the best air purifier for your needs.