What is the difference between a sega and a sega 16 bit?

The Sega Master System/Mark III was Sega's 8-bit counterpart to the Nintendo Entertainment System (NES or Famicom, depending on where you live). It uses a Z-80 8 bit processor and did well in Europe and Brazil (where as of a few years ago it was STILL the best selling system of all time in that country), and was a miserable failure in the other two "major markets", the US and Japan. Had a handful of gems, most notably the hugely influential Phantasy Star and Wonderboy III.

Sega's 16-bit platform (Using a Motorola 68000 CPU) was the Genesis (or Mega-Drive, if you live anywhere but the US), and it, unlike its predecessor was a genuine global success (especially in the Western world, where it bested the SNES in Europe and kept it a close fight down to the wire in the States). It, of course, is most well known for introducing the world to Sonic the Hedgehog (back when he didn't suck), and for unleashing the demon that is EA(sports) on the world. Madden, NHL and FIFA series all got their starts here more or less*.

So yea, completely different systems.

Sega 16

They are both sixteen bit game method. Genesis is made by Sega, at the same time SNES is made by way of Nintendo. The Genesis used to be more robust than the SNES, as evidenced through Sonic the Hedgehog. Photo intelligent, the Genesis was once also better.