Dinobot Island is the name given by Spike Witwicky to an island on Earth that can only be accessed by flying through a mysterious energy column floating over the ocean. It is primordial, populated by dinosaurs, and rich in volcanic energy.´
The island's position in time is unclear: It may be somehow trapped in a temporal bubble, isolated from the timestream; or the energy column may be a gateway to the entire prehistoric world, with the island being simply the nearest bit of land. Most evidence points to the former theory, but altering the island will produce strange temporal effects elsewhere in the present.
At any rate, what it sorely lacks in explanation, it makes up for in woo dinosaurs!
The Transformers cartoon
After scouting some strange power readings, Bumblebee and Powerglide encounter an unknown island in the middle of the ocean. Bumblebee is attacked by a prehistoric flying dinosaur which Powerglide manages to save him from, after which they examine the island briefly before leaving after another dinosaur attempts to attack them. Bumblebee makes a comment about how the state of the island is exactly how the Earth was 100 million years ago, so the immediate depiction of a Tyrannosaurus standing perfectly still and upright next to a sauropod should be considered historically and scientifically accurate.
Returning to Autobot headquarters, they inform Optimus Prime of the find while a test of the Dinobots is made. It's decided that the Dinobots are simply too chaotic to work safely at headquarters but Bumblebee suggests the newly discovered island as a new home for the Dinobots to which Prime agrees. As Spike, Powerglide and the Dinobots head off to the island, they are shadowed by Laserbeak who transmits his findings to Megatron. Megatron takes his Decepticons to the island where they begin to tap the island's energy reserves; much to Starscream's objections as he notes various instabilities on the island. The Dinobots eventually learn of the Decepticon presence on their island and attack but Megatron uses the Dinosaurs to stampede and force the Dinobots off a cliff and into a tar pit.
The draining of the island's energy reserves results in numerous time rifts forming all around the planet, bringing denizens from Earth's past into the present, including barbarians on mastodons, pirates, and cowboys. The Autobots learn of the Decepticon presence on Dinobot Island and lay siege to Megatron's forces there. The Decepticons manage to gain the upper hand and are about to win when the Dinobots return and bring their new friends, the dinosaurs, to the Autobots' aid. The Decepticons are defeated by the dinosaurs and retreat. Optimus Prime and the Dinobots destroy the Energon cubes collected which releases the energy back to the island, thus replenishing it.
However, the island did not remain under solely Autobot control. Twenty years later, Galvatron sent Trypticon to Dinobot Island to recuperate after his first battle with Metroplex, and the Autobots were completely unaware. It was there that Octane enlisted Trypticon's help in his plan to use Carbombyan oil to take over the Decepticons. All of this was only mentioned in passing, so no details are known about the state of the island or the extent of the Transformers' continued use of it.