title: Why does Mathematica use an underscore when defining parameters?
body: <p>For example if I was defining the following function</p>
  
  <pre><code>exprod[n_] := Expand[Product[x + i, {i, 1, n}]]
  </code></pre>
  
  <p>Then why is the underscore after the variable n, necessary in the function definition? Where does this style come from or is it specific only to the Mathematica programming language?</p>