Hyperdrives allowed ships to enter the realm known as hyperspace, a Hyperdrive didn't actually change the speed of the ship, it just opened a portal to hyperspace, and formed a stable tunnel through hyperspace. After that, the ship’s ion engines propelled it through hyperspace, although they used little fuel in hyperspace.
A ship’s speed in hyperspace was determined by its Hyperspace Velocity Rating, (or HVR), which was equivalent to 10 parsecs per standard hour. The hyperdrive used fuel to maintain the hyperspace tunnel, if the ship ran out of fuel the tunnel collapsed and the ship would transit back into realspace.
Hyperspace’s physics were different from those of realspace; the light speed barrier simply didn't exist there. Acceleration in hyperspace was instantaneous, when a ship’s engines engaged in hyperspace it was instantly accelerated to its maximum velocity as determined by its HVR.
Energy screens were necessary in hyperspace, without them the ship’s hull would be sheared off.
Hyperspace tunnels appeared to be a tunnel of swirling green plasma. Hyperspace hypnosis occurred when someone stared into the hyperspace tunnel for too long, causing them to defocus and lose awareness of their surroundings. To combat this, many military vessels darkened their windows when they were in hyperspace.
Hyperspace tunnels were in straight lines; changing destinations was as simple as changing the ship’s heading; the tunnel reformed to fit the new heading.
Hyperspace was a violent dimension, eddies and currents could throw a ship off course, so the governments of the galaxies created “Hyperspace Routes” or “Hyper-routes” which were charted tunnels of hyperspace. A ship didn't even need a hyperdrive to travel in a hyper-route, the tunnels were held open at either end by large space stations which sent small drones through the tunnel to stabilize it. Hyper-routes were the only hyperspace tunnels that were not in straight lines, they curved as necessary.
Objects in realspace produced gravity-shadows in hyperspace, normally these were not a problem, but the larger the gravity well, the more dangerous its shadow was. Planets and stars had to be taken into account when plotting a hyperspace course, as colliding with a gravity shadow usually resulted in the ship's destruction.
Hyper-routes had an HVR, used in the same way as a ship’s HVR. Most routes leading to either of the galactic cores had an HVR of 8 or more. “Rural” routes tend to have HVRs of 5 or less.