In the Custom Portal users can filter their data by selecting values in Filter Blocks, from within a Tableau Dashboard, or even via the System JavaScript API. These selections are stored in the user's browser and automatically applied on future page loads until a different selection is made.
Often you will wish to give your users the ability to remove, or clear, their filter selections. In this case you can use a Clear Filters Block.

Note: When using a Cascading Filters Block, a Clear button is already provided so there is no need to use a Clear Filters Block. See the Cascading Filters Block documentation for more information.