Benefit Fraud is a Fraud committed in order claim state benefits or other services belonging to another or entitled by the government to people who meet a certain (typically) socioeconomic criteria.
The most common form of benefit fraud is when a person receives benefits, but continues or begins employment. Another common form of fraud is when the receivers of benefits claim that they live alone, but they are financially supported by a partner or spouse.
Ref.: http://www.inbrief.co.uk/personal-finance/benefit-fraud