Outbound Route Filtering (ORF) is the BGP capability which is negotiated between BGP neighbours during a session setup.
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If during a session setup process BGP ORF ( Outbound Route Filtering ) capability is exchanged , one peer can send a signal to its BGP neighbour about desired or unwanted prefixes.
Assume you are receiving a full BGP table from the neighbouring Internet Service Provider , if they support ORF as a BGP capability and agree with you to use it then you can tell to neighbouring BGP router by sending an update that you don’t want particular BGP prefixes without calling ISP and explaining what you want.
It may seem an easy task but from operational point of view , it can really shorten your time and effort.