Domestic Violence Context: Emotional abuse in domestic violence situations can include verbal abuse, intimidation, humiliation, and manipulation. This can involve threats, controlling behavior, or actions meant to undermine the victim’s self-esteem or sense of safety.

Child Abuse Context: For child abuse, emotional abuse includes behavior that causes significant harm to a child’s emotional development. This can involve persistent belittling, rejection, threats, or exposure to severe marital discord.

Indicators: Signs of emotional abuse might include depression, anxiety, severe behavioral changes, or a diminished sense of self-worth in the victim.

Legal Considerations: In legal proceedings, emotional abuse can be harder to prove than physical abuse, but evidence might include testimonies, documented patterns of behavior, and expert assessments.

But how bad does it have to be to be considered abuse

Idk
Enough that it has long term effects I think?
Im not an expert in this and emotional abuse can be harder to identify than other types of abuse however if you suspect your being emotionally abused id recommend doing research.
Also , to my understanding, at any point if you feel unsafe around them you are allowed to call the cops even if it isnt necessarily abuse.