title: Difference between key and index in arrays
body: <p>I'm confused with the terms <code>index</code>, <code>key</code> , <code>key-value pair </code> &amp; <code>element</code> with respect to arrays in TCL or say any other programming language in general.</p>
  <p>I know that we use <code>index</code> for non-associative arrays and keys for associative arrays , but don't understand why.</p>
  <p>Can anyone help me understand the exact meaning (difference between them) and usage of these terms.</p>
  <p>Thanks</p>