A massive, circular ring with an inner track of 39 symbols representing star constellations, capable of sending people and objects hundreds of thousands of light years via an interstellar conduit called a wormhole. The Stargate, constructed millennia ago by the Ancients, is made of the alien mineral naquadah and weighs about 64,000 pounds.
One side of the gate holds nine equally-spaced, V-shaped locking mechanisms, or "chevrons," capable of locking at least seven constellations in place via a freely-spinning inner track. The first six glyphs lock down a point in space, while the seventh represents the point of origin. When the seventh chevron locks, an unstable energy vortex emerges from the gate, incinerating everything in its wake. Once the vortex is gone and the event horizon is established, outbound travel may commence. Once objects have exited the other side, the Stargate has the capability of shutting itself off.
The Stargate is essentially an enormous superconductor, capable of harnessing power from a wide variety of energy sources, especially electricity. The inner track is a safety feature. When the gate has absorbed enough energy this track will unlock, allowing a manual dial in case something dire has occurred to the D.H.D.
The Stargate network extends beyond our own galaxy, and includes many thousands of gates. Most gates are paired with a dial-home device (D.H.D.), by which a user dials an address to another world. The S.G.C. does not have a D.H.D., and instead has rigged a computer system to access the gate's systems and dial addresses.
In the Pegasus Galaxy, some Stargates have been placed in space in orbit of planets, rather than on their surfaces. Rather than using a connected D.H.D., space-based gates are powered by three power nodes, and dialing is accessed by a panel on a ship.
Perhaps the oldest gates in existence are in the style of the Destiny Stargate, and those gates manufactured and placed on planets by automated Ancient vessels in various galaxies beyond our own. This gate seems cruder, spinning entirely (without an inner track) and without moving chevrons.
Gates deposited on planets in distant galaxies by automated seed ships have a smaller range. An address dialed from one planet is able to reach several in close proximity, but unlike the more modern gates generally cannot reach every other Stargate in that galaxy.
"Stargate" the Movie - Dr. Jackson uncovers the seventh symbol, the point of origin, and opens the Stargate for the first time in nearly 50 years.
Solitudes - Another Stargate, predating the Egyptian gate, is accidentally discovered in Antarctica.
The Fifth Race - O'Neill boosts power to the Stargate allowing for an eighth chevron to lock on to gate coordinates in the Ida galaxy, far further than any previous lock.
Nemesis - SG-1 transports the Stargate to Thor's ship to escape a Replicator infestation; the Antarctic gate is removed from storage and set up at the S.G.C.
Redemption, Part 2 - Anubis's weapon, originally constructed by the Ancients, forces Stargate Command to hoist the Antarctic gate from Cheyenne Mountain into deep space, roughly three million miles from Earth, where it is destroyed. The Russians "loan" the U.S. the Egyptian gate.
Avenger 2.0 - Dr. Felger's lab assistant, Chloe, deduces a potential of 63 billion Stargates in the universe.
Beachhead - SG-1 discovers that the Ori are capable of creating massive "Supergates" in space, large enough for whole fleets of ships to pass through.
Ripple Effect - Carter explains that typical gate travel is not instantaneous. On average it takes approximately zero point three seconds.
Air, Part 1 - Evacuees from Icarus Base discover a totally new kind of Stargate when they arrive on the Destiny, which appears to pre-date the Milky Way and Pegasus Gates.
Lost - After they are left behind on a planet Eli, Matt, and Chloe use the network of Stargate in a distant galaxy to try and get back within range of Destiny.
Incursion, Part 1 - The Lucian Alliance uses a Milky Way gate to make the second successful connection to Destiny using the ninth chevron.
Cloverdale - Sgt. Greer dials the gate repeatedly while under attack from alien creatures, using the unstable energy vortex to protect Scott and Chloe.
Twin Destinies - Eli's ill-advised plan to dial Destiny's Stargate from inside a star has unforeseen repercussions when a solar flare sends the entire ship back in time.