Which of the following defines thirdhand smoke?

Thirdhand smoke refers to the residual nicotine and other chemicals that remain on surfaces and in dust after tobacco has been smoked. This can include cigarette butts, walls, furniture, clothing, and even vehicles where smoking has occurred. Over time, these toxic substances can react with common indoor pollutants to create even more harmful compounds.

The other options describe different aspects of smoking but do not accurately capture the concept of thirdhand smoke. For instance, the smoke exhaled during smoking pertains to mainstream and secondhand smoke, which are both actively present in the air at the moment of inhalation and exhalation. A person smoking a cigarette pertains to the act of smoking itself but does not reflect the lingering effects of tobacco in the environment. Thus, only the residual nicotine on surfaces specifically encapsulates the essence of thirdhand smoke.