What counts as cheating on your partner? Sexting someone else? Sharing a peck on the lips? Having sex in secret?
To an Australian psychologist, anything from sending heart emojis to quietly chatting online with someone who isn't your partner can be described as "microcheating". Other apparent indiscretions include saving a person's number in your phone under a different name, speaking to an ex-partner, or sharing a private joke.
Melanie Schilling told HuffPost Australia that microcheating involves "seemingly small actions that indicate a person is emotionally or physically focused on someone outside their relationship".
"If your partner is having private conversations or online chats that he/she quickly shuts down when you enter the room; if they are reaching out to an ex to mark an anniversary or other significant shared, intimate event; perhaps they are offering compliments to other guys/girls that they don't say to you; or maybe they meet up with someone of the opposite sex under the guise of a business meeting, when you discover no business was actually done... these are all signs to look out for."
The idea of microcheating rapidly sparked a debate on Twitter, with many arguing that by defining infidelity outside of sexual physical contact and policing a partner's behaviour - including something as vacuous as their emoji use - could be a sign of abuse.
Ammanda Major, head clinical practice at the relationship charity Relate told IBTimes UK that constantly accusing a partner of cheating is often used by abusive partners as a method of control.
"Behaviours that consistently seek to control, humiliate and distress a partner are inappropriate and now a criminal offence," she added.
"Sometimes people can be overly suspicious of friendships and feel they threaten the relationship. Having friends of whatever gender or sexual orientation, spending time with them and speaking to them on social media is perfectly normal and reasonable."
She added: "A couple's ability to support and encourage this in each other is usually the sign of a healthy, caring relationship."
Controlling behaviour is at the heart of all domestic abuse, and overlaps with sexual and financial abuse, according to the charity Living Without Abuse. As well as violence, the website warns readers to be wary of actions including forbidding contact with friends and family; as well as constant texting and calling and checking on where the victim is, and what they are doing.
But what if a person feels they perhaps are hiding a friendship with another person because they secretly enjoy flirting, or feel it turning into something romantic?
Major advises those who feel the need to conceal friendships from their partner to consider the root cause.
"You shouldn't feel you have to share absolutely everything with your partner but if you're finding yourself having to do things in secret then you may want to ask yourself why. Is it because your partner is unreasonable or controlling, in which case, think about seeking support, or is it because you aren't being honest with yourself about your true motivation?
"It's fine to have friends and confidants but knowing when it might be going too far and reflecting on what that might be about is the key," she added.
Interestingly, research by Relate suggests that what people define as cheating varies hugely, and that it doesn't have to involve sexual contact. The charity's Let's Talk About Sex report found that almost a fifth of men didn't consider passionately kissing someone else to be cheating, while 45% of women aged between 16 and 24 said that flirting is betrayal.
"Instead of asking yourself whether what you're doing is cheating or micro-cheating, consider whether it's likely to be something that detrimentally affects your relationship with your partner," suggested Major. "Labels like cheating and micro-cheating aren't very useful – what matters is how that behaviour makes you and your partner feel."