Controls how long (value in seconds) the client is allowed to be gone before the session is reclaimed. Typically takes care of the client crashes. Working together with cleanup cycle (default is 5sec). Worst case scenario, a session can be idle for timeout + cleanup cycle before the timeout is detected.
When elapsed the browser will be released for another test to use. To remove the timeout completely, specify -timeout 0 and the hub will never release the node. (Can be used when doing step-by-step debugging of client code)
Default value is 30sec.
Replaces the -nodeTimeout parameter starting from selenium v2.21.0

See also:
https://code.google.com/p/selenium/wiki/Grid2
https://code.google.com/p/selenium/wiki/RemoteWebDriverServer