A payload in Metasploit refers to an exploit module. There are three different types of payload modules in the Metasploit Framework: Singles, Stagers, and Stages. These different types allow for a great deal of versatility and can be useful across numerous types of scenarios. Whether or not a payload is staged, is represented by ‘/’ in the payload name. For example, windows/shell_bind_tcp is a single payload with no stage, whereas windows/shell/bind_tcp consists of a stager (bind_tcp) and a stage (shell).
Singles are payloads that are self-contained and completely standalone. A Single payload can be something as simple as adding a user to the target system or running calc.exe.
These kinds of payloads are self-contained, so they can be caught with non-metasploit handlers such as netcat.
Stagers setup a network connection between the attacker and victim and are designed to be small and reliable. It is difficult to always do both of these well so the result is multiple similar stagers. Metasploit will use the best one when it can and fall back to a less-preferred one when necessary.
Windows NX vs NO-NX Stagers
Reliability issue for NX CPUs and DEP
NX stagers are bigger (VirtualAlloc)
Default is now NX + Win7 compatible
Stages are payload components that are downloaded by Stagers modules. The various payload stages provide advanced features with no size limits such as Meterpreter, VNC Injection, and the iPhone ‘ipwn’ Shell.