title: What is constant factors and low-order term in algorithms?
body: <p>In the following video, there is an explanation of asymptotic analysis:
  <a href="https://class.coursera.org/algo-004/lecture/169" rel="nofollow noreferrer">https://class.coursera.org/algo-004/lecture/169</a></p>
  
  <p>But I can't understand what is "low-order term" and "constant factor" itself? (it is at the 4th minute of the video).</p>
  
  <p>The merge sort is <code>6n*log2(n)+6n</code>. Why <code>6n</code> is the low-order term and 6 is <code>constant factor</code> in here? Do these terms have concrete definition?</p>