A social worker was someone who worked with individuals, groups, and societies in an effort to improve the overall life conditions of the client or population they were engaged with.
Edith Keeler was a social worker at the 21st Street Mission on Earth in the 20th century. She was described thusly in a 1930 newspaper article. (TOS: "The City on the Edge of Forever")
While living homeless in the year 1996, Captain Braxton complained that social workers came around all the time giving unwanted advice. (VOY: "Future's End")