If a host sends a TCP segment with the RST flag set, it means:

A.
The receiver should send all data in the reassembly buffer to the application receiving it immediately.

B.
The receiver should reset the session.

C.
Any routers between the source and destination hosts should reset the state of the connection in their buffers.

D.
The receiver should make certain its send buffer is pushed onto the wire.

Explanation:
http://hhi.corecom.com/tcp-operation.htm