One of my students is looking at Sex and Relationships Education. Most of the articles on 'romantic' relationships during 'adolescence' are based on studies carried out in the US. As such, we're having to engage with a whole new vocabulary, including the two words in scare quotes above, and also 'dating' and 'group dating'.
The following forum discusses the meaning of 'dating' in the American context, compared with the situation in the UK and Canada:
http://ask.metafilter.com/mefi/28643Although some of the contributors argue that the discussion is essentially due to different language usage, I think there is more to it than that. It appears that the notion of 'dating' in the US context refers to a concept that is very much cultural in that it differs between the US and the UK (with, as I understand it, the situation in Canada and Australia being more similar to that in the UK).
Dating seems to describe relationships that have a couple of defining characteristics:
1) Low commitment and care-giving responsibilities
2) No absolute expectation of relationship exclusivity
In terms of commitment, in the UK we might use the expression "I was seeing him/her" to indicate a (relatively new?) relationship with little mutual commitment. This particular difference is perhaps primarily semantic: in the US the word 'dating' is used; in the UK, we say 'seeing'.
However, it is apparently relatively common in the US to 'date' a number of people for a period of up to around 6 months. According to the age and expectations of those involved, these relationships may have a physical aspect including kissing, sexual intercourse, etc. It seems as though it is expected that beyond this time, one of these relationships will become 'exclusive'. This might occur via conversations concerning 'exclusivity' of the 'chosen' relationship, or may simply be assumed (potentially leading to misunderstandings!)
As such, the major difference I can see between the situation in the US and the UK therefore revolves around the notion that in the UK, monogamy is always assumed (unless otherwise negotiated) as soon as any form of physical sexuality takes place, or perhaps even before; in the US this is not the case, and according to the context, initial non-monogamy may almost be expected.
The very fact that the Americans who have contributed to this forum use the words 'monogamy' and 'exclusivity' quite liberally indicate a difference with the UK where any mention of 'monogamy' either refers to a comparison with polygamy, or other practices such as swinging that are usually considered 'weird'. I don't think these words wouldn even really be used in the UK in the context of 'having an affair' because they seem incongruent with the secrecy surrounding affairs.