User Tasks for Evaluation: Untangling the Terminology Throughout Visualization Design and Development

User tasks play a pivotal role in evaluation throughout visualization design and development. However, the term `task' is used ambiguously within the visualization community. In this position paper, we critically analyze the relevant literature and systematically compare definitions for `task' and the usage of related terminology. In doing so, we identify a three-dimensional conceptual space of user tasks in visualization. Using these dimensions, visualization researchers can better formulate their contributions which helps advance visualization as a whole.