You can encounter other options than actual column names in the column selectors.
(Column Names) When more than one column is specified on a continuous axis in a visualization (such as the value axis in a bar chart), the option (Column Names) becomes available for selection in column selectors on other axes. The term (Column Names) represents the names of these columns. If (Column Names) is selected on an axis, the names of the columns will be treated as categories on the axis.
(Subsets) When you have filtered data in your analysis, it is possible to display the following three categories; the data that is filtered to, the data that is filtered out, and the entire data. These categories can be compared in a single visualization by selecting the (Subsets) option in a column selector.
(Row Number) You select the (Row Number) option in a column selector, when you want each row in the data table to be shown individually in a visualization.
(Row Count) You select the (Row Count) option in column selectors when you want to display how the rows are distributed between different categories in a data column.
(Axis values) In column selector menus, you can encounter different (Axis values) options, for example, (Value axis values), (Color by values), and (X values). Such a non-column option represents the resulting values on the axis in question. It is especially useful for referring to axes with multiple columns.