Can somebody please tell me what exactly a ghost page is? How can we create a ghost page? I have very little information about it, like ghost pages are used by firms for promotional purposes.
Simply put, it's deliberate deception of search engines for SEO purposes. It's bad practice.
Longer answer:
Say you're optimizing your cheese-selling site. You want people to find it when googling "cheese". So you would create a bunch of content where "cheese" has a high keyword density of 12 % or so. Of course, this renders the page pretty useless for the user - the user just wants an image, some data on the cheese and a header, but that isn't SEO-friendly enough for you.
So, you'll create all the content you need for your SEO purposes and serve that up - in an if/else statement. Basically, if the visiting computer is GoogleBot, you'll serve up all that great text. If it's not GoogleBot, you'll serve up correct content.
So a Ghost Page (more accurately known as Shadow Page) is pretty much just a (bad) way for you to get ranking that you don't deserve.