An open marriage is a type of marriage where both partners have agreed to allow each other to have sex with other people. This is the metaphorical equivalent of having your sexual cake and eating it too.
There is a spectrum of definitions for an open marriage, but the
general understanding is that the partners involved are not only aware
of each other's desires, but trusting that said activities will not
result in jealousy or other problems that will destroy the marriage.
Usually there are spoken and unspoken rules that define the boundaries
of what is acceptable (e.g., "not in our marital bed", "no sleeping with
my sister", etc.), in order to prevent jealousy as well as problems
involving other people who might know the couple outside of their sexual
activities.
The following examples of the range of experiences in open marriage:
One or both partners have sex with other people, but keep the
details quiet. This type of relationship often happens when one partner
feels he or she is not sexually fulfilled, but does not desire ending
the marriage.
Both partners have sex with other people specifically during times of separation (like business trips or military deployment).
Both partners enjoy rich sexual activities outside of the
marriage, but limit it to one night stands, so no emotions get brought
in.
One partner allows the other to have sex with others because
he or she cannot, usually due to physical limitations such as illness or
a disliking of sex. .
Polyamory, where extramarital sexual partners are integrated into family life.
Polygamy is technically an open marriage, but in practice the women are not usually active with anyone other than a husband.
Swinging, which has its own gigantic spectrum of practices, involving both partners (either participatory or simply watching).
