In which context are you referring to an SID?

In unix context, sometimes a process is killed with the process session ID SID. For ex, with "pkill" command you could kill the processes with the given session id. A session id of 0 translates to pkill's own session.

SID is majorly talked about in a database context. Supposing, you have more than one instance of Oracle running on the same box with different /ora/home paths, then choosing the SID assigns you the correct instance you want to work with, and includes it in your UNIX path.

You may get more viwes if you could try the search option on this forum..good luck!