Oracle BI 11g which we hadn't seen before, the "Prompt User" operator on a dashboard prompt. I'm not sure exactly when the feature was introduced but we first saw it in OBIEE 188.8.131.52.2 BP1.
Previously the type of "operator" used on a dashboard prompt was fixed by the report developer e.g. "Is equal to / is in", so an end user could not change it once the dashboard prompt had been published on to the dashboard page.
However, this new feature provides flexibility by allowing the end user choose which type of operator should be used to filter on the values selected in the actual prompt:
Configuration is easy: within the dashboard prompt editor, you simply open up the properties for the relevant prompt and set the "Operator" to "* Prompt User":