Temporal uncertainty is a crossing point of temporal and error-aware geographical information systems. In Geoinformatics, temporal uncertainty is of the same importance as spatial and thematic uncertainty of geographical information. However, until very recently, the standard organizations of ISO/TC211 and FGDC subsequently claimed that temporal uncertainty is one of geospatial data quality elements. Over the past decades, temporal uncertainty of geographical information is modeled insufficiently. To lay down a foundation of logically or physically modeling temporal uncertainty, this paper is aimed to clarify the semantics of temporal uncertainty to some extent. The general uncertainty is conceptualized with a taxonomy of uncertainty. Semantically, temporal uncertainty is progressively classified into uncertainty of time coordinates, changes, and dynamics. Uncertainty of multidimensional time (valid time, database time, and conceptual time, etc.) has been emphasized. It is realized that time scale (granularity) transition may lead to temporal uncertainty because of missing transition details. It is dialectically concluded that temporal uncertainty is caused by the complexity of the human-machine-earth system.