The default receive window size in bytes. Refer to the following discussion of per-route metrics for setting a different value on a per-route basis. See tcp_recv_hiwat_minmss and tcp_max_buf also.
2048 to 1,073,741,824
Note that this is the default value. An application can use setsockopt(3SOCKET) SO_RCVBUF to change the individual connection's receive buffer.