All the credit is due to the RFC’s authors: A. Azimov (Qrator Labs & Yandex), E. Bogomazov (Qrator Labs), R. Bush (IIJ & Arrcus), K. Patel (Arrcus), K. Sriram.
What are route leaks in the context of BGP routing
According to RFC7908: “A route leak is the propagation of routing announcement(s) beyond their intended scope. That is, an announcement from an Autonomous System (AS) of a learned BGP route to another AS is in violation of the intended policies of the receiver, the sender, and/or one of the ASes along the preceding AS path. The intended scope is usually defined by a set of local redistribution/filtering policies distributed among the ASes involved. Often, these intended policies are defined in terms of the pair-wise peering business relationship between ASes (e.g., customer, transit provider, peer).”