Earth-82
The Transformers are a species of sentient, living robotic beings (mostly) originating from the distant machine world of Cybertron. The stories of their lives, their histories, and most especially their wars have been chronicled across many different continuities in the vast multiverse.
The designation "Transformer" stems from the species' generally-shared ability to transform, to change their bodies at will, rearranging their component parts from a robotic primary mode (usually, but not always, humanoid) into an alternate form; generally vehicles, weapons, machinery, or animals. In some continuities this ability to transform is innate to all members of the species, in others it was a wartime innovation that was adopted by most, but not all, of the populace.
While this species is commonly known throughout the galaxy as "Transformers", the technical term for these beings is Cybertronians, which they generally use to refer to themselves. Other, less-frequently used terms to refer to beings from Cybertron include Cybertronic or simply Cybertron.

Autobots

The Autobots are one of the primary factions in the Transformers mythos. They usually find themselves defending both their own race and other species against the Decepticons and upholding justice and freedom throughout the galaxy.
A generally heroic, honorable group, they tend to be dedicated to peace, and feel a need to protect other races from the Decepticons. As a result, they are usually Transformers who change into non-combat oriented alternate modes such as domestic vehicles, cars, trucks, or rescue vehicles. This is not always the case, however, as their ranks certainly contain ne'er-do-wells, malcontents, and unsavory types, and the necessities of war have led many to adopt more combat-oriented alternate forms. While the Autobots have usually found themselves outnumbered by the Decepticons, the Autobots have always had home-field advantage, having not only the humans' military support, but also having more places on Earth to fall back on, while the Decepticons are entirely unwelcome on Earth.
Key concepts that repeat throughout most continuities are the use of the name Prime (or a variation thereof) to denote Autobot leadership, and the existence of an artifact of great life-giving power, usually referred to as a "Matrix", traditionally held by their leader.
The collective noun for Autobots is an "exaltation".

Optimus Prime Autobot Commander	Prowl	Ironhide	Jazz	Jetfire

Bluestreak	Silverstreak	Smokescreen	Sideswipe	Sunstreaker

Tracks	Mirage	Sandstorm	Skids	Hound

Wheeljack	Perceptor	Ratchet	Inferno	Red Alert

Trailbreaker	Hoist	Grapple	Bumblebee	Beachcomber

Brawn	Cliffjumper	Gears	Huffer	Outback

Pipes	Swerve	Windcharger	Powerglide	Sea Spray

Cosmos Interplanetary Transport	Warpath Demolitions Specialist	Omega Supreme Heavy Assault Station	Bulkhead Space Bridge Engineer

Espionage Team

Blaster	Eject	Rewind	Ramhorn	Steeljaw

Dinobots

Grimlock	Slag	Sludge	Snarl	Swoop

Aerialbots

Skybolt	Fireflight	Skydive	Air Raid	Slingshot

Superion

Protectobots

Hotspot	Blades	First-Aid	Groove	Streetwise

Defensor

Fire Convoy Team

Located in Japan and investigating a team of Destructicons led by Gigatron, Fire Convoy is leading a separate team from the main Autobot Force, and has recently arrived, pledging to stop the Destructicons from rejoining Megatron's main force with whatever energy they collected.

Fire Convoy Team Commander	God Magnus Second-in-Command	Mach Alert	Speedbreaker	Wild Ride

Artfire	Counter Arrow	Crosswise	Eagle Killer	Indy Heat

Ox	Wars	Wrecker Hook	A.I.

Build Team

Build Hurricane	Build Typhoon	Build Cyclone	Build Boy	Build King Combination

Rail Team

Rail Racer	Railspike	Rapid Run	Midnight Express Combination

Decepticons

The Decepticons are one of the primary factions in the Transformers mythos. They are typically concerned with such things as conquering Cybertron, defeating the Autobots, amassing large quantities of energon, developing powerful weaponry, and beating people up. Not necessarily in that order.
Unlike the Autobots, whose leader is a Prime bearing a Matrix, the Decepticons are led by the most powerful of their ranks. This tends to cause some conflict, given how generally every Decepticon thinks that they're the most powerful. Also, the Decepticons are not exactly the most compassionate beings in the universe, but not all fight for greed. More than a few have a sense of honor, while others believe that Cybertron would be better protected by aggressive expansion. Ultimately, the Decepticons desire to protect their homeworld, even if it is at the expense of others. Usually.

Megatron Decepticon Leader	Octane	Astrotrain	Blitzwing	Barricade

Knock Out Medic	Bombshell	Kickback	Shrapnel	Nightbird

Demolishor	Lockdown	Lugnut	Dirt Boss	Tidal Wave

Blackout	Crumplezone	Landquake	Strika Vehicon Commander	Thunderblast

Vehicon Drone Ground Commander	Vehicon Drone Ground Soldier	Vehicon Drone Ground Soldier

Espionage Team

Soundwave Intelligence Officer	Laserbeak	Ravage	Rumble	Frenzy

Buzzsaw	Reflector

Seekers

Air Commander Starscream	Skywarp	Thundercracker	Hotlink	Nacelle

Slipstream	Dirge	Ramjet	Thrust	Vehicon Drone Seeker

Vehicon Drone Seeker	Vehicon Drone Seeker

Constructicons

Bonecrusher	Hook	Long Haul	Mixmaster	Scavenger

Scrapper	Constructicons Gestalt Devastator

Stunticons

Motormaster	Breakdown	Dead End	Drag Strip	Wildrider

Stunticons Gestalt Menasor

Combaticons

Onslaught	Blast Off	Brawl	Swindle	Vortex

Bruticus

Destructicons

An offshoot of the Decepticons, led by Gigatron, who traveled to the Colonies to gather both Predacons and Decepticons, forming a powerful unit of combatants, tracking down some sort of forbidden energon. They have traced some of it back to Earth, and have been pursued by Fire Convoy's team. Gigatron has not rejoined the main Decepticon forces, due to seeking out this Energon, but he used the excuse to wipe out the Autobots chasing him before coming to America to rejoin Megatron, to keep them from reinforcing Optimus's forces.