Subjectivism is an approach to doing science which acknowledges and makes room for subjectivity. In traditional positivistic and macro-structural sociology, the subjectivity of the researcher and of the subjects is seen as something to be avoided.
The preferred stance for the researcher is objectivity or objectivism, making the assumption that the observation of the world can occur in a neutral fashion without being influenced by theory or cultural or personal assumptions. The subjectivity of the subjects being studied is to be avoided since it is assumed that peoples lives are shaped by structural and cultural forces of which the subject may be unaware.
More recent sociology (e.g. Interpretive Theory, Ethnomethodology) is open to acknowledging the subjectivity of both researcher and subjects. One might study, for example, the ways in which the coroner interprets notes, slash marks, family environments, or medical histories, in an effort to arrive at an interpretation of a death. The coroner's subjectivity then is a valid area for investigation.
Similarly one might be interested in how the scientist too is also involved in arriving at an interpretation and examining how this is shaped by the subjective assumptions made. Subjectivism is thus an approach to doing science which both acknowledges and makes room for subjectivity.