What classification describes a condition of extremely low body weight, with a BMI of 18.5 or lower?

The classification of "Underweight" is defined by a Body Mass Index (BMI) of 18.5 or lower. BMI is a standard measurement used to assess body weight in relation to height, and those who fall into the underweight category are identified as having a significantly decreased amount of body mass. This classification highlights health risks associated with insufficient weight, which can include nutritional deficiencies, weakened immune function, and other health complications.

In contrast, the other classifications denote higher BMI ranges: "Obesity" indicates excessive body weight, while "Normal Weight" and "Overweight" encompass ranges above the underweight threshold. Understanding these categories is crucial for identifying health issues and ensuring that individuals receive appropriate care based on their body weight status.