Nowadays, when someone asks what the concept of "ideology" meant to Marx, the common reply is that ideology is the false consciousness we have about an entity or event. In other words, only the epistemological or negative meaning suggested. However, few have bothered to check if that is what ideology really meant to Marx or if other meanings (e.g., a sociological or neutral significance) coexisted in his work. This study explains the epistemological or negative meaning, which sees ideology as a problem related not only to the misconceptions one has about the material world but also to reproduction of the dominant system. The neutral meaning is presented as well. It indicates ideology can be a set of ideas or values that are not necessarily false, and can motivate emancipatory practices.