Some Scandanavian words for the term "introduction" are
- Danish — introducerede
- Norwegian — introduserte
- Icelandic — introdecerede
- Swedish — kyrkotagen
- Finnish — kyrkotagen (Swedish language time period)
The custom dates back to the Bible where Moses taught that after a mother had born a child, she was basically not to have visitors or be out in society for about six weeks minimum.
Eventually, the command to let the mother stay home, rest, and not mingle with society for a time period was interpreted to mean that the mother had sinned by giving birth, and she had to be cleansed of that sin via a formal ceremony held in a church meeting. In older times, the mother might literally have had to crawl up the aisle of the church, begging forgiveness for her sin. In later time periods, she would walk up to the front of the church, the minister would take her hand, and he would say she was cleansed and formally welcome her back into society.
For some time periods in all the Scandinavian countries, the date of the "mother's introduction" back to the church is recorded. This is important because this ceremony and recording of the date could take place also in case of stillbirths. If there is more than a two or three year gap between the births of children in your Scandinavian family, finding your ancestor's father or mother's name in the introductions without an accompanying christening entry could indicate a stillbirth.
There was not always six weeks from the time of the birth to the introduction of the mother, so the introduction date cannot be used to figure back to a birth date for the child. It took place when the mother was physically well enough to get out again. Sometimes, the mother would be introduced before the child was christened; often the two events took place on the same Sunday.
In time periods before the printed record format asked for the mother's name, she was often not recorded in the actual birth or christening entry except as "wife." However, the minister may have listed her by name in the introductions. Sometimes this date of the mother's introduction or "churching day" (kyrkotagen) is simply listed to the side or at the bottom of the christening, instead of being listed out in a separate record.
If you do not find an introduction after the known birth of a child, it's possible that the mother died in childbirth or shortly thereafter.
Any woman who bore a child, whether married or not, would have to go through the introduction ceremony. In the case of an unwed mother, she would also go through an absolution process, which might be recorded separately in the parish register.