A caseworker is a person — usually a social worker, or someone in a very similar job — who looks after particular people or families and their problems. The word names the worker, not the work. (The work is casework.) A school gloss that sounds like “the work a social worker does” is describing the job; a caseworker is the human being who does it. You can say a caseworker, the caseworker, our caseworker. That person has a caseload, and often a casebook. It is a job title, a little formal. In ordinary talk people may just say social worker, but caseworker is the more exact word when you mean “the one assigned to this family.”