In Custom Dashboards, along with the default Project, Environment, and Time Range filters, you are now able to add your own global filters.
Global filters can be added for any of the properties available when using widget builder (see: Widget Builder Filters). These filters, shown at the top of the page, let you ask questions specific to your dashboard. As an example, you might filter an Outbound HTTP Request dashboard to show you how many requests are made to a specific domain.

This functionality is available now for accounts with Early Adopter Features enabled.