Loneliness is one of the least conceptualized psychological phenomena (Fromm-Reichman, 1959). The growing awareness that social relations play a fundamental role in psychological well-being has led mental health researchers to integrate work on loneliness and social support. This has influenced most of the definitions we have of loneliness nowadays. Thus, when defining loneliness, there is a tendency to focus on social distress, which is just one aspect of the experience. Various disciplines have provided different definitions: some have focused on the multifaceted nature of loneliness (addressing the interaction between specific behaviors, emotions and thoughts), while others have focused primarily on cognitive aspects. In such definitions, loneliness is also regarded as a subjective experience, but the subjective aspect is often described as something "private," which obscures the experiential features that are essential to loneliness. In this article, I review the most dominant definitions of loneliness and address some of their underlying assumptions and problems. I propose that a starting point for arriving at better definitions and distinguishing between types of loneliness is to focus on the temporal, embodied and attentional dimensions of the phenomenon.