Www.firemountaingems.com What's The Difference Between A Cabochon & The Actual Gem?

What's the difference between a cabochon & the actual gem? - www.firemountaingems.com

I want to buy this little gem ...
http://www.firemountaingems.com/details. ...

However, in bold at the top of that, "Drop 34x16mm, 18x14 mm cabochon says
I googled cabochon and said it is a jewel that has been formed. Who's who?

How big is the jewel of them all?