title: What is singleton in PHP?
body: <p>This question may be really a silly question for many.  But, i could not find the exact answer for it.</p>
  
  <p>What is singleton class in PHP?</p>
  
  <p>I went through many tutorials, still do not understand exact meaning of it.
  What I understand is that, it cannot be instantiated more than once. The object will be shared.
  What does that really mean? Suppose the singleton is implemented for database connection, does it mean, that if 'A' is access the site and logging in. Meanwhile say 'B' tries to login and B will not be able to login until A logout and releases the object? </p>