What's the advantage of having an SSD in a laptop, rather than a hard disk?

SSD or HDD? There’s no straight forward answer to this question, each buyer has different needs and you have to evaluate the decision based on those needs, your preferences, and of course budget. Even though the price of SSDs has been falling and right now there is a tight supply of HDD drives the price advantage is still strongly with HDDs. But if performance and fast bootup is your top consideration, and money is secondary, then SSD is the way to go.

SSD? what is full name. As per me hard disk is best thing to have.

According to me, I prefer hard disk over SSD. It depend on our choices and need.