I believe this is the definition that is more or less accepted in "Western" society:
adultery: Voluntary sexual intercourse between a married person and a partner other than the lawful spouse.
(Variations)
Western society have nothing to do with Christianity Jesus never agreed to people having sexual intercourse.that is man made laws, they have even allowed people to have sex with same sex which the bible calls a gross evil sin.
However, we also hear it used differently ...
Some people think that the actual sexual act does not have to be performed for a married person to be committing adultery.
true fornication is all about cheating in secrect or in public and that is evil otherwise no one would object to having their partners having sex with others.
Some believe that it is only the married party that is committing adultery if the other partner is single... not both - others disagree ...
Others (primarily Muslims ?) have been seen to use the word "adultery" to mean any sexual relations outside of marriage - even if both parties are single.
Big difference?
in Islam we see that being the same. however the punishement is very different
What does it mean to you?
I should know better
since i have been in those circles before. all i can say is that it is evil and no one likes to see their partners messing around or potential partner as being a cheat or some one who does not care.
If someone is in a bad marriage and falls in love with someone else, are they committing adultery?
In Islam there are many ways to resolve that issue and divorce is the last resort
Do they have to act on it?
What about couples that are separated - emotionally? physically? legally?
If one of them gets involved with someone else during the separation, is that adultery?
In my book yes unless they are divorced
Do they have to actually do it for it to be considered so?
without 100% facts one should stay away from Gossip and ill talk, everyone is innocent until proven guilty
What kind of people do this?
Normal people who are far from God, they are called followers of Satan
What do you think?
I think that Marriage is good and should be the only way to a happy life that respect people and God