title: What does `m_` variable prefix mean?
body: <p>I often see <strong><code>m_</code> prefix used for variables</strong> (<code>m_World</code>,<code>m_Sprites</code>,...) in tutorials, examples and other code mainly related to game development.</p>
  
  <p>Why do people add prefix <code>m_</code> to variables?</p>