Symbols are the points that can be drawn over image of datapicker. Symbols can be directly created by mouse right click over the image. Symbols are mainly of two types, with and without error-bar depending on the type of curve they belong.
Every curve of datapicker can have its own symbol style that can be changed in the Symbols section of dock widget. "SelectAndMove" mouse mode can be used to select multiple points/symbols and can be moved by using navigation keys.