What is a Solid State Drive (SSD) and how is it different from a Hard Drive (HD)?

To start, let's tackle the question of exactly what is an SSD and what are the benefits. The easiest way to describe this is as an SSD being an array of flash memory modules similar to a flash drive which are controlled in such a way that, once the computer is shut off, it retains its memory unlike normal computer RAM. The SSD is totally different than RAM, in that it is made of flash memory rather than volative memory, thus bringing into existence the term 'solid state memory'. With computer memory (RAM) when you turn off the computer it "forgets" what was stored there. With an SSD, like a hard drive, the idea is of course it permanently stores and remembers the data you put on it. That data can be anything from an operating system to a music file.

There are no moving parts within a solid state drive, which is the critical difference between that and the older hard drive technology which must rely on mechanical operation to store and retrieve data. In order to access or store data, the HD relies on a metal disk to spin at a speed of up to 7200 revolutions per minute and an arm that extracts or places the information on the disk.
What are the advantages of SSD?

The advantages of a SSD are numerous. First and foremost the sheer speed of the SSD is the most obvious and overpowering feature. Its reasoning is simple. There is no requirement for the disk to spin and the arm to find the exact position of the information it is retrieving. Let's think of the SSD as a book. One simply has to look at the index and then retrieve the information knowing the proper chapter and page. 
Quicker startup, incredible performance, no moving parts, less heat, longer battery life, incredible reliability and durability will soon enough conquer the obstacles of price, storage restrictions and availability.