What is the difference between Signal-to-Noise Ratio (SNR) and Noise Reduction Rating (NRR) in the context of audio equipment?

Signal-to-Noise Ratio (SNR) measures the quality of the signal compared to the level of background noise, indicating how clear the audio is. Noise Reduction Rating (NRR) quantifies how much external noise is reduced by a device, such as headphones or earplugs, to improve the listening experience.