What is measured in decibels is sound intensity or loudness. The decibel scale is logarithmic, measuring sound pressure levels relative to a reference level, usually the threshold of hearing for humans. For instance, a whisper is approximately 30 decibels, normal conversation about 60 decibels, and sounds over 130 decibels can cause immediate hearing damage. This scale helps quantify and compare sounds across various environments, from quiet libraries to noisy construction sites. Understanding decibels is crucial for audiology, environmental monitoring, and noise control measures in urban planning.