There is no set distinction between a singer and a vocalist, and people use the terms interchangeably. In a technical sense, there is little difference between a singer and a vocalist. However, some people disagree, and there are competing definitions. For example, one could say that a rapper or anyone that uses non-traditional vocal styles is a vocalist but not a singer. In another sense, some people define a vocalist as a classically trained singer. In this definition of a vocalist, you focus technique and adherence to the composition. A singer, on the other hand, is a vocal performer that tries to convey the emotion of the composition. You are judged less by your technique. You can highlight this difference by looking at a rock singer versus an operatic vocalist.
