These are all questions that are crucial when learning about working with abused women.
There isn't just one definition of abuse, because abuse is simply put as "an attempt to control the behavior of another person. It is a misuse of power which uses the bonds of intimacy, trust and dependency to make the victim vulnerable." (As stated by Nova Vita - Domestic Violence Prevention Services). The United Nations Declaration on the Elimination of Violence Against Women describes violence against women as "a manifestation of historically unequal power relationships between men and women". As you can see, I have highlighted the words "control" and "power" because those are the main reasons as to why abuse occurs.
One important point to mention is that abuse is not one isolated incident but a series of past incidences that create fear. Violence is intentional, meaning that the abuser doesn't just lose control and accidentally harm or threaten their partner. An abuser may act in such manners as they have learned that these actions create results. However, abusers do not just pick up abusive behaviors. Rather, they learn that these behaviors are acceptable from an early age. Many male abusers learn that is is appropriate for a man to control his wife and to enforce his power and control over her through violence. They learn this mainly through observation and experience (culture, family, etc.). What they learn is then reinforced when the community fails to sanction them for this behavior.
Just as inequality between men and women contribute to domestic violence, domestic violence contributes to reinforcing gender inequality. In the Declaration on the Elimination of Violence Against Women, the United Nations denounces that domestic violence as one of the "crucial social mechanisms by which women are forced into subordinate [positions] compared with men".
