For some people cheating is as simple as getting intimate with someone else.
But as technology impacts the way we form relationships, communicate and meet people, what constitutes a betrayal becomes more blurred and complex.
These days it's not just kissing someone that could make your partner jealous. Talking to crushes online and even having an active dating profile could make your lover green with envy.
Here's what people think counts as cheating and what doesn't.
A dating site for people who are already married polled members to determine which actions are considered adulterous.
Forming a deep emotional bond with someone else was considered the biggest betrayal, by 55 per cent of those surveyed.
This was followed by sending naked pictures or erotic messages to someone else.
Almost 30 per cent of people asked think maintaining an online dating profile is adulterous - as is spending time with an ex.
For other people more subtle actions are classed as cheating, like casual flirting, going out to dinner with someone of the opposite sex, talking to their ex or fantasizing about someone else - but these were in the minority.
Ultimately, what's most important is that couples define with each other where the line is so it's clear if it's been crossed.
"People make a conscious choice to cheat, it's not typically something that people fall into," says Dr. Tammy Nelson, sex and relationship therapist and author of The New Monogamy: Redefining Your Relationship After Infidelity.
"Despite defining what infidelity means to one another, one or both people in a relationship could still make the choice to seek an extra-marital affair when their needs aren’t being met.
"An alternative conversation to have is one that outlines what it is that each partner needs from the other to feel happy and satisfied in the relationship, and how to talk about it when they don’t feel that."