A Pulse Drive is a spaceship's primary means of traveling interplanetary distances, separating simple short-range orbiters from true deep space boats.
A pulse drive works on the principles of inertia reduction, which reduces a ship's resistance to motion in a particular direction to practically zero. When combined with a high-impulse, low-efficiency rocket motor to give a big initial thrust and keep the ship moving, the resulting pulse drive allows the ship to travel sixty times faster than normal reaction drives.
There are three main drawbacks to the pulse drive, the first of which is that the velocity achieved isn't "real." So long as the pulse drive is on the ship will keep moving, but when it turns off the ship will return to its original velocity. Reaction drives are therefore necessary to get the ship moving for at least part of it's journey.
The second is that the inertia reduction works only along the drive axis. While a very gradual course correction can be made while the pulse drive is functioning, including performing a gravity slingshot around a planetary body, making a radical course change requires the ship to turn off the pulse drive, orient the ship along the new heading, and re-initiate it. Since this method is very fuel intensive most pilots carefully chart their course before beginning a journey, including accounting for any necessary slingshot maneuvers.
The final drawback is that pulse drives are very imprecise mechanisms - in the few seconds it takes a spaceship to turn off it's pulse drive it may travel over 10,000 miles before returning to its original velocity. Less of a problem in the vastness of space, using pulse drives around a planetary body is much harder and less safe than simply relying on reaction drives.
Pulse drives are classified by how fast they propel a ship, from the very slow found on bulk cargo carriers to the fastest found on racing yachts and couriers. Even the slowest pulse drives (Class 1) are able to get a ship from one planet's moon to another in less than a day, while the fastest (Class 10) can travel between any one of the Central planets in a day or cross the entire Verse in twenty-five.