A more thorough explanation:

Definition: Deadbeat mom is a slang term used to describe a mother who has not paid or is behind in making child-support payments. This term is not used as frequently as deadbeat dad or deadbeat parent because more men than women fail to support their children financially after divorce. It can also refer to an able-bodied mother whose income is derived from welfare payments instead of gainful employment.

• After the divorce, the court ordered the mother to pay child support, but she hasn't paid a dime. She's a deadbeat mom.
• She's been on welfare for years and hasn't made any effort to find a job. She's a deadbeat mom.

The first example illustrates a deadbeat mom who has not fulfilled her financial obligation to her children. The second example illustrates a deadbeat mom who relies on welfare instead of working to support her family.