At least old-fashioned philanderers knew where they stood. For them, only an extramarital affair was considered cheating.
In the modern, digital age, however, it takes an awful lot less to wreck a relationship. Welcome to the world of "micro-cheating".
An academic has declared it to be the new method for couples to tear each other apart. According to psychologist Dr Martin Graff, from the University of South Wales, all it now requires is the click of a computer button for a partner to be considered unfaithful - and with all the same consequences as a full-blown affair.
Examples of micro-cheating include checking the social media accounts of former partners; sending emoji such as hearts and flowers to other people; and saving mobile phone contact details of someone from the opposite sex under a false name.
In short showing a high level of "digital" interest in someone outside the existing relationship can constitute micro-cheating.
"It can be something as simple as repeatedly 'liking' someone's posts on Instagram or commenting on someone's Facebook," said Dr Graff.