A Metal Gear is a bipedal nuclear tank which features in most of the Metal Gear games. The first made Metal Gear is Metal Gear Raxa which was known as an ICBMG, then there was Metal Gear TX-55 and Metal Gear D. The next Metal Gears were Metal Gear Rex and Metal Gear Ray. After those they finally perfected the Metal Gears and made what is codenamed Metal Gear Gekko.
If you mean story wise then I believe it goes: Metal Gear Solid 3: Snake Eater Metal Gear Metal Gear 2: Solid Snake Metal Gear Solid Metal Gear Solid 2 Metal Gear Solid 4 But I may be wrong, and that isn't counting either of the Portable Ops games.
metal gear solid1, metal gear solid 2 sons of liberty, metal gear solid 3 snake eater, and metal gear solid 4 guns of the patriots.
Metal Gear Solid 4: Guns of the Patriots
There has been no confirmation of a Metal Gear and Metal Gear 2 remake. They are playable on Metal Gear Solid HD Collection in the Metal Gear Solid 3 portion, but thats the only thing that would be considered a remake right now.
Metal Gear Solid, Metal Gear Solid 2: Sons of Liberty and Metal Gear Solid 3: Snake Eater
the metal wears down from the gear turning metal against metal
Metal Gear Online happened in 2008.
Metal Gear Arcade happened in 2010.
Metal Gear Solid happened in 1998.
Metal Gear Acid happened in 2004.
Metal gear (MSX) came out in 1990 Metal Gear Solid (PSOne) came out 1994
As of 2012, there exist three Metal Gear Solid games with the exception of Metal Gear Rising: Revengeance for the Microsoft Xbox 360. They are Metal Gear Solid 2: Sons of Liberty, Metal Gear Solid 3: Snake Eater, and Metal Gear Solid: Peace Walker. They are part of the Metal Gear Solid: HD Collection, and can also now be purchased separately.