## Core Concept
The gross fertility rate (GFR) is a demographic measure that calculates the number of births that occur in a population over a specific period, usually a year. It is expressed as the number of births per 1,000 women of childbearing age (typically 15-44 or 15-49 years). This measure provides an estimate of the fertility level in a population.

## Why the Correct Answer is Right
The correct answer, **B. Number of births per 1000 women of reproductive age per year**, accurately defines the gross fertility rate. The GFR is indeed calculated as the number of live births per 1,000 women aged 15-44 or 15-49 years in a given year. This measure does not take into account the age distribution of the women, making it a "gross" rather than "specific" rate.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it refers to the total fertility rate (TFR), which is the average number of children a woman would have in her lifetime based on the current fertility rates of a population.
- **Option C:** This option is incorrect because it describes the general fertility rate (GFR sometimes used interchangeably but specifically defined as births per 1,000 women of reproductive age), which, although similar, might not precisely match the definition provided in B.
- **Option D:** This option is incorrect because it seems to conflate the definition with another demographic measure, possibly the crude birth rate, which is the total number of live births per 1,000 people in a population per year.

## Clinical Pearl / High-Yield Fact
A key point to remember is that the gross fertility rate does not account for the age-specific distribution of women within the reproductive age group, which can vary significantly between different populations. This makes it a somewhat crude measure compared to age-specific fertility rates but still useful for quick assessments of population fertility.

## Correct Answer: B. Number of births per 1000 women of reproductive age per year