Glossary
Short definitions of terms used on this site, each taken from or directly supported by the cited source.
BMI (body mass index)
A person's body weight in kilograms divided by the square of their height in meters, according to the U.S. Centers for Disease Control and Prevention (CDC). It is a screening measure that does not distinguish fat, muscle and bone mass.
Underweight
A BMI below 18.5 for adults, in both the World Health Organization (WHO) 2000 table and the CDC's adult categories.
Normal range / healthy weight
The BMI range 18.5 to 24.99 (WHO calls it "normal range") or 18.5 to less than 25 (the CDC calls it "healthy weight").
Overweight and pre-obese
WHO's fact sheet defines overweight in adults as a BMI of 25 or more. In WHO's 2000 table, "pre-obese" is the part of that group from 25.00 to 29.99. The CDC uses "overweight" for 25 to less than 30.
Obesity and obesity classes
A BMI of 30 or more in adults, according to WHO's fact sheet and the CDC. WHO's 2000 report and the CDC both split it into class I or 1 (30 to under 35), class II or 2 (35 to under 40) and class III or 3 (40 or more).
Estimated Energy Requirement (EER)
The average dietary energy intake predicted to maintain energy balance in an adult of a defined age, sex, weight, height and level of physical activity, as defined by the National Academies of Sciences, Engineering, and Medicine (NASEM) (2023).
Total energy expenditure (TEE)
The abbreviation NASEM uses for the energy a person uses, measured in kcal per day. NASEM's tables state that for weight-stable adults, EER equals TEE.
Physical activity level (PAL)
The measure NASEM uses to place adults in one of four categories: inactive, low active, active and very active. Each category covers a range of PAL values, for example 1.00 to below 1.53 for inactive adults.
Adequate Intake (AI)
A reference amount that the Institute of Medicine set for total water when it judged that an average requirement could not be estimated. For total water it is based on median U.S. survey intake and should not be read as a specific requirement.
Total water
Water from drinking water, beverages and food together.
Last menstrual period (LMP)
The first day of a woman's most recent menstrual period. The American College of Obstetricians and Gynecologists (ACOG) counts the estimated due date from it, and MedlinePlus measures gestational age from it.
Estimated due date (EDD)
By convention, 280 days after the first day of the LMP, according to ACOG. It is an estimate, and only about 1 in 20 women give birth on their due dates.
Gestational age
The age of a pregnancy in weeks, measured from the first day of the last menstrual period to the current date, according to MedlinePlus. ACOG writes it as weeks and days, so "36 and 3/7 weeks" means 36 weeks and 3 days.
Trimester
One of three stages of pregnancy. ACOG puts the first from the first day of the LMP to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks 0 days to 40 weeks 6 days.
Full term
ACOG defines full term as 39 0/7 through 40 6/7 weeks. Early term is 37 0/7 through 38 6/7, late term is 41 0/7 through 41 6/7 and postterm is 42 0/7 and beyond.
Naegele's rule
A way to estimate the due date by adding 7 days and then 9 months to the first day of the last menstrual period, described by StatPearls as equivalent to 280 days.
Sleep cycle
The repeating pattern of REM and non-REM sleep. The U.S. National Heart, Lung, and Blood Institute (NHLBI) says the cycle starts over every 80 to 100 minutes, with usually four to six cycles per night.
REM and non-REM sleep
The two phases of sleep that NHLBI names. During REM (rapid eye movement) sleep, your eyes twitch and your brain is active. Non-REM sleep includes stage 1 (transition between wakefulness and sleep), stage 2 and stage 3 (deep sleep or slow-wave sleep).