title: what is parameter level in getsockopt?
body: <p>I got the following link: <a href="https://stackoverflow.com/questions/21515946/sol-socket-in-getsockopt">SOL_SOCKET in getsockopt()</a></p>
  
  <p>But it is really confusing for me. One replied that the <code>SOL_SOCKET</code> means the socket layer. What is the socket layer? Are there any other options available for that parameter?</p>
  
  <p>What happens if we pass the <code>SOL_SOCKET</code> parameter and what does the <code>SOL</code> stand for?</p>
  
  <p>I am using UNIX.</p>