There's no such thing as a 'mutually abusive' relationship, therapists say. With abuse, one partner is always in power.

• Relational abuse can show up in the form of physical violence, name-calling, or stalking.
• In an abusive dynamic, even if both people exhibit toxic behaviors, there is always a primary aggressor, experts say.

During public court hearings for the defamation lawsuit involving Johnny Depp and Amber Heard, the former couple's marriage therapist testified that their relationship involved "mutual abuse."

Laurel Anderson, a clinical psychologist who used to counsel Heard and Depp together, said Depp told her Heard "gave as good as she got" and would initiate fights "if she felt disrespected." Anderson also mentioned that Heard's father was physically violent towards her.

But this type of "mutual abuse" dynamic doesn't exist, because it ignores the inherent power dynamic in abusive relationships, according to therapists Insider spoke to.

"An abusive relationship requires one person to take control of the other. A relationship can be toxic on both sides — neither person is supportive of the other, they both sham each other. But abusive relationships are unidirectional," Lori Beth Bisbey, a psychologist and intimacy coach with 30 years of experience, said.

There are many forms of abuse in relationships

Abuse is defined as "a pattern of behaviors used by one partner to maintain power and control over another partner in an intimate relationship," according to the National Domestic Violence hotline.

Abuse is not just limited to physical violence. It can show up in many forms, such as emotional and verbal abuse —which can include threats and insults — sexual coercion, financial abuse, or stalking.

Whatever form it takes, the aim of the perpetrator is to exert power and control over their partner.

While two partners can act in toxic ways towards each other and push their relationship into unhealthy territory, abusive dynamics require a primary aggressor, Ruth Glenn, president and CEO of the National Coalition Against Domestic Violence, told NBC.

She said if someone reacts in a physically, mentally, or emotionally intense or violent way to abuse, it means they're defending themselves, not being an abuser in return.

All emotionally abusive relationships are toxic, but not all toxic relationships are abusive

From the outside looking in, two people engaged in an abusive relationship may both appear to exhibit toxic patterns, but that doesn't mean there is "mutual abuse."

"I don't believe in mutual abuse," Glenn told NBC. I don't believe that two parties decide to meet in the kitchen and box it out. It just doesn't sound right, reactive abuse. I'm going to abuse you as a reaction? No, I'm going to defend myself as a reaction."

Defensive tactics can show up in many forms, like name-calling and physically pushing back, psychologist Betsy Usher told NBC.

However, once defensive actions start to occur outside of moments where there is no perceived threat, it's no longer self-defense, therapist Darcy Sterling, a clinical social worker and host of E! Network's "Famously Single," said.

"Self-defense happens in the actual moment of being on the receiving end of violence or operating under the belief that violence is imminent. It's all about timing and imminent threat," she said.