Ascendant genealogies: genealogies which start from a person alive today and work backwards to record those in their main line of ascent.  

Baby Boom: the big spike in births which began during, and continued after, the second world war across Europe, North America, Australia and New Zealand. 

Childbearing ages: Demographers define the childbearing ages as between age 15 and age 49. Although some women can give birth at younger or older ages, such births are very rare. 

Civil Registration: The state-run recording of births, deaths and marriages. Civil registration started in England and Wales in 1837 and in Scotland in 1855. 

Cohort: a group of people born in a particular year or group of adjacent years. 

Cohort rate: a demographic rate which is calculated from the experience of cohorts. For example, a cohort total fertility rate measures the average number of births experienced by women in a particular cohort over the course of their childbearing years. The disadvantage of this type of measure is the need to wait until the cohort is no longer at risk of the event (in term of fertility until the cohort has reached age 50) before it can be measured. 

Collateral kin: relations which are not in an individual’s direct line of descent, e.g. aunts, cousins, nieces. 

Crude birth rate: the number of births in a population in a year, per 1,000 people. 

Demographic transition: The change over time from high birth and death rates to low birth and death rates. 

Descendant genealogies: genealogies which select a person in the past and follow their kin forward in time. 

Direct maternal death: death of a woman from a cause directly related to pregnancy or childbirth, such as post-partum haemorrhage or puerperal fever. 

European Marriage Pattern (also known as the North-West European Marriage Pattern): a customary system of family formation in North-West Europe characterised by the formation of new households on marriage (neolocal marriage), ages of marriage which were both relatively late and responsive to economic circumstances, a relatively large proportion of people never married, and the presence of life-cycle service (young people spending several years during their late teens and early twenties earning money by working for a non-family member, often living in their household). 

Family reconstitution: the reconstruction of families by linking the baptisms, marriages and burials in parish registers. 

Fecundity: in demographic usage, fecundity refers to the ability to conceive. 

Fertility: in demographic usage, fertility refers to childbearing success (i.e. women who have had at least one child are defined as fertile). 

Hutterites: a communal ethnoreligious branch of Anabaptists, mainly living in Western Canada and the upper Great Plains of the United States. This North American group of Hutterites has the highest documented fertility rates of any single population and has been used as a benchmark for high fertility. 

Indirect maternal death: death of a woman within 42 days of the end of a pregnancy, from a cause not directly related to the pregnancy, such as infectious or non-communicable disease. These are included in maternal mortality as the chance of dying from such causes is likely increased by the fact that a woman is pregnant or recently delivered. 

Inter-birth interval: the time gap between successive births. 

Maternal death: The WHO defines a maternal death as the death of a woman while pregnant or within 42 days of the end of a pregnancy (usually a birth), from causes directly related to pregnancy or childbirth (such as post-partum haemorrhage or puerperal fever) or from a cause which could have been aggravated by the pregnancy (such as tuberculosis or heart disease), but excluding accidental or incidental causes of death. Some definitions include deaths up to 60 days (or longer) after the end of a pregnancy. 

Maternal mortality ratio: The number of maternal deaths divided by the number maternities (pregnancies or birth events). In many situations (such as where stillbirths are not uniformly recorded) the number of live births is used instead of the number of pregnancies. 

Menarche: a woman’s first menstrual period, before which she is very unlikely to be able to conceive. 

Menopause: the cessation of menstruation, after which conception is not possible. 

Non-marital fertility rate: the number of births outside marriage divided by the number of unmarried women (usually including both single and widowed women) of childbearing ages (age 15 to 49). 

Non-marital fertility ratio: the number of births outside marriage as a percentage of the total number of births. 

Parish Registers: The local handwritten registers of each church recording the baptisms, marriages and burials. When the Church of England split from the Roman Catholic Church in 1538, each parish priest was required to keep such records, and they remain useful sources of demographic information until the introduction of civil registration in 1837. 

Period rate: a demographic rate which is calculated using the experience of a cross section of people of different ages. These experiences are spliced together to create the outcome which would hold if a person were to go through the experiences of each age group in turn. For example, a period total fertility rate is calculated by calculating the number of births per woman in the last year for women in different five-year age groups, and then assuming that those are the rates that a hypothetical woman would experience across her childbearing lifetime. Period rates have the advantage that they can be calculated for short time periods and recent years, but they can be quite volatile. Period fertility rates, in particular, can be affected by changes in the timing of births. 

Pre-marital pregnancy: Births conceived before marriage but born within marriage. Where such births are identified using parish registers, these are usually births taking place within eight months of a marriage ceremony. As there was generally a gap between birth and baptism, some infants born nine, or even 10, months after a marriage may also have been pre-maritally (pre-nuptially) conceived. However, any infants conceived soon after marriage who were born pre-term might have been born less than nine months later.  

Reeve: a management official who was an unfree tenant of the manor and received a rent acquittance as his wage. Over the 14th century, these officials were increasingly replaced by serjeants, who typically received a stipend in cash and grain (and were not necessarily tenants).   

Replacement rate: the level of fertility at which a population exactly replaces itself from one generation to the next. In places with low fertility and mortality, replacement level fertility is taken to be 2.1 children per woman, but in places or eras with higher mortality it is higher. 

Sibship size: the number of children in a sibling group. 

Total fertility rate: the average number of children women have over the course of their childbearing lives (generally defined as age 15 to 45).