Population (under enumeration): members of all private settled households, institutional and collective, whose usual place of residence is located in Iran at the time of enumeration, as well as members of all private unsettled households. Foreign delegations, diplomatic corps and their families are excluded.  However, Iranian delegations and members of Iranian diplomatic corps and their families at Iranian embassies in foreign countries are included in the population under enumeration.
Private household: persons living together in one residence, sharing their living expenses and eating together constitute a household. A person living alone also forms a private household.
Private settled household: a household living in a permanent residence which was made from hard materials, fixed tent, hut, straw hut, etc.
Private unsettled household: a household not living in a permanent residence at the time of enumeration. This group of households includes three types:
1. households either moving from one area to  another or living under tents outside cities  and villages; 
2. households that do not live in a permanent place and change their living place continually, such as gypsies;
 3. households that do not live in a specific place and usually pass the night at parks, in ruined places, under bridges, etc.
Institutional household:  persons who share   a common objective or characteristics living together in an institution which is responsible for their accommodation, (residential place with services and facilities) according to permission or specific regulations. Examples of institutional households are: barracks, garrisons, student dormitories (excluding those for married students) managed by universities, asylums, etc.  
Collective household: persons who live together because of having common conditions (mainly common characteristics) and manage life affairs together. 
City (urban area): every geographical area with a municipality.
 In censuses before 1365, all Shahrestan centres (irrespective of their population size) and places with a population of 5000 persons and more were considered as city.
Village (rural area): one or more contiguous places and lands (agricultural or non-agricultural) located outside city borders and having independent registered or conventional boundaries. Any village inhabited by one or more households at the time of enumeration is considered as an "inhabited village", otherwise, it is considered an "uninhabited village".
Population  settled in urban areas: population settled in urban areas in any administrative division of Bakhsh, Shahrestan, Ostan or country, is the population of all cities located in the division concerned; and the population of each city is the total number of all private settled, institutional and collective household members whose usual place of residence is located in that city at the time of enumeration. 
Population settled in rural areas: population settled in rural areas in any administrative division of Dehestan, Bakhsh, Shahrestan, Ostan or country, is the population of all villages located in the division concerned; and the population of each village is the total number of all private settled, institutional and collective household members whose usual place of residence is located in that village at the time of enumeration. 
Unsettled population: unsettled population in any administrative division of  Shahrestan, Ostan or country, is  the population of  all private unsettled households who were enumerated in the division concerned.
Head of Household:  A    member    of     the household who is acknowledged the head, by the other household members. It is noteworthy that the head is responsible for bearing all or major part of household expenditures or make decision on how the household incomes should be spent.
The head is not necessarily the oldest member of the household, but can be a male or female member who is usually more than 10 years old. It is obvious that in one-person households, the only member of the household is considered the household head. 
Age: the number of completed years since the date of birth. 
Mean age: average age of the population.
Median age: the age which divides the population into two equal groups in number.