Tooltips are an elegant way of providing more contextual information and detail to data points on a visual. The following image shows a tooltip applied to a chart in Power BI Desktop.
When a visualization is created, the default tooltip displays the data point's value and category. There are many instances when being able to customize the tooltip information would be useful, and would provide additional context and information for users viewing the visual. Custom tooltips enable you to specify additional data points that display as part of the tooltip.
To create a customized tooltip, in the Fields well of the Visualizations pane, simply drag a field into the Tooltips bucket, shown in the following image. In the following image, four fields have been placed into the Tooltips bucket.
Once Tooltips are added to the field well, hovering over a data point on the visualization shows the values for those fields in the tooltip.
You can further customize a tooltip by selecting an aggregation function or a Quick Calc by selecting the arrow beside the field in the Tooltips bucket, and selecting from the available options.
There are many ways to customize Tooltips, using any field available in your dataset, to convey quick information and insights to users viewing your dashboards or reports.