Abstract: Uncertainty always exists in satellite navigation process and results, which includes random errors, systematic errors, outliers and colored noises etc. There are many different measures for evaluating the quality of the navigation results, such as precision, accuracy, reliability and uncertainty, and so on. In practice, the accuracy, precision and error itself are often confused by the users, so are the uncertainty and the uncertainty measures. Especially, the accuracy is often followed several times standard deviation or error percentage. For example, the user range accuracy (URA) index is often followed standard deviation. In this paper, the user range error (URE) is redefined based on the uncertainty concept. Then the URE and URA are distinguished and their relationship is obtained. The uncertainty is distinguished from the uncertainty measure. The often used reliability concept in geodetic adjustment is introduced and described. At last, several notes on the concept of error, precision, accuracy, URE and URA are given.