What is a route filter?

A. a list of prefixes that can be configured in a policy

B. a single prefix that is configured separately, and can be referenced in a policy

C. a list of prefixes that is configured separately and can be referenced in a policy

D. a single prefix that can be configured within a policy

A route filter is a collection of match prefixes. When specifying a match prefix, you can specify an exact match with a particular route or a less precise match. You can configure either a common action that applies to the entire list or an action associated with each prefix.

References: http://www.juniper.net/documentation/en_US/junos16.1/topics/usage-guidelines/policy-configuring-route-lists-for-use-in-routing-policy-match-conditions.html