explanation of reverse_tcp vs. reverse_ord_tcp and memory execution

[jeffs at speakeasy.net (Jeffs)]

Is there a document or reference somewhere that explains the differences 
between all the different meterpreter reverse connections?

Like what's the difference between the reverse_tcp which I've used 
successfully many times, and reverse_ord_tcp which I've yet to get working.

Also, if I successfully upload a reverse binary to a target computer and 
the module that does the uploading also executes it, naturally the AV is 
alerted because the binary has been written to disk and that's the AV's 
territory.

Is there a way to get the binary or facsimile of the binary to execute 
in memory on the target machine thereby bypassing the AV's hooks?

Thank you.