Social Welfare and Social Work are two different terms. Social Welfare have subjective definitions, and it's different among one person to one person to define it. These are some definition to understand what is "Social Welfare".
"Organization that draws its support from a broad base within the community, along with schools, churches, and hospitals. More generous contribution limitations apply to donors. Generally, aggregate income from the four previous years must be received from individual contributions or governmental sources, and not more than one-third may consist of investment income and unrelated business income."
"Social welfare or public charity, organized provision of educational, cultural, medical, and financial assistance to the needy. Modern social welfare measures may include any of the following: the care of destitute adults; the treatment of the mentally ill; the rehabilitation of criminals; the care of destitute, neglected, and delinquent children; the care and relief of the sick or handicapped; the care and relief of needy families; and supervisory, educational, and constructive activity, especially for the young."
Among the Greeks and Romans public assistance was given chiefly to those holding full citizenship. It was early connected with religion, as among the Hebrews and, from them, among the Christians and later the Muslims. The Christian Church was the main agency of social welfare in the Middle Ages, supplemented by the guilds. Later, national and local governmental agencies, as well as many private agencies, took over much of the charitable activity of the church.
See R. E. Asher, United Nations and the Promotion of the General Welfare (1957); H. Kraus, ed., International Cooperation for Social Welfare (1960); A. C. Marts, Man's Concern for His Fellow-man (1961); S. Mencher, Poor Law to Poverty Program (1967); J. F. Handler, Reforming the Poor (1972); E. W. Martin, Comparative Development in Social Welfare (1972); W. I. Trattner, From Poor Law to Welfare State (1974).