Bidirectional Forwarding Detection (BFD) is a protocol intended to detect faults in the bidirectional path between two forwarding engines, including physical interfaces, sub-interfaces, data link(s), and to the extent possible the forwarding engines themselves, with potentially very low latency. It operates independently of media, data protocols, and routing protocols.

BFD is basically a hello [...]]]> From the Mikrotik WIKI:

Bidirectional Forwarding Detection (BFD) is a protocol intended to detect faults in the bidirectional path between two forwarding engines, including physical interfaces, sub-interfaces, data link(s), and to the extent possible the forwarding engines themselves, with potentially very low latency. It operates independently of media, data protocols, and routing protocols.

BFD is basically a hello protocol for checking bidirectional neighbor reachability. It provides sub-second link failure detection support. BFD is not routing protocol specific, unlike protocol hello timers or such.

What does this mean? It is a way to detect a failure between two routers that does not depend on the routing protocols they speak.  For example, you can run BFD “on top of” OSPF, BGP, etc.

Some Caveats:
-Requires Router OS 4.4
-Does not support echo or authentication.  If you are talking to a Cisco device you need to disable echo on the interface the Cisco uses to talk to the Mikrotik.