UNIX related

Might vary by OS. For Solaris:

tcp_conn_req_max_q0 is the maximum number of connections with handshake incomplete. A SYN flood attack could only affect this queue, and a special algorithm makes sure that valid connections can still get through.
tcp_conn_req_max_q is the maximum number of completed connections waiting to return from an accept call as soon as the right process gets some CPU time.

more is available at http://www.sean.de/Solaris/tune.html
http://www.sean.de/Solaris/tune.html#tcp_conn_req_max_q
http://www.sean.de/Solaris/tune.html#tcp_conn_req_max_q0

As Fossil describes and notes the difference very well, but note that the values that these parameters vary form one unix system to another. So if you have IBM AIX at the red book library tunning for AIX, or OS/390 OMVS check out at the red books at the instalation and tunning , Unix system services for OS/390 manuals, or at the memo to users at chapter installing Open System services (at yoursystemparmlib(BPXOINITxx)) parameters. In some other unix systems these parameters are mostly theused with there default values, as far I have seen.
The setting up of these values are in case of using a LPAR IBM system to provide enough physical memory and swap memory so the address spaces of the OS can share the same device for the non Open System (MVS).

Hope it helps