Abuse is when one person treats another person cruelly and violently. It can be in the form of physical violence or verbal aggression which can harm and cause emotional stress to someone.
On several occasions, we fail to recognize abuse, especially if it is not physical. We neglect the fact that a person may be hurting from the inside due to a stressful relationship.
That said, there are different types of abuse including physical, sexual, verbal, emotional, financial, etc.
Emotional abuse is very common in romantic relationships and may get overlooked since the signs can be hidden under pretentious guise. However, it can be as traumatic and difficult to overcome as physical abuse.