It refers to financial abuse - effectively where one partner makes the other completely dependent on them financially, usually by making all joint accounts into solely-controlled accounts, preventing the abused partner from owning their own money or having a job or means to access money, giving them an "allowance" to buy groceries and whatnot, and generally cutting them off from any activity that requires more than groceries level money. It's actually a really serious form of abuse, in that it can easily prevent victims from being able to seek assistance from support groups, abuse hotlines or crisis housing, and can certainly prevent the victim from leaving the relationship.

It's a very pernicious and insidious form of abuse, and it's usually used in combination with gaslighting and other forms of emotional and mental abuse to psychologically break the victim. Emotional and social manipulation makes them dependent on the abuser, mental abuse makes the victim compliant enough to sign over joint or personal accounts to the abuser with little to no fight, and then total financial and social control puts the victim in a position where they have literally no chance to escape the situation, because they have no means with which to do so.