It is the fast forwarding path for OFFw, which caches the entries recently matched in OFFw.
OFFw. It maintains flow table of entries, in which each entry contains a set of packet fields to match and the corresponding actions to perform (e.g., forwarding, dropping, and modifying header).
In the event when a switch does not find a match in OFFw, the packet is forwarded to the controller through OFCh.