studentuscd, in the motor-gearbox world that I live in, backdriveable simply means that the load side of the powertrain can transmit torque backward thru it to the motor. This commonly occurs when using a motor or motor-brake to decelerate a high inertia load. It can also occur when the load side of the system is being "forced" mechanically, as in taking a robot arm and pushing it with your hand into a position with the motor power off or, as in pushing a manual transmission car to start the engine. I think this is the meaning you are presenting here.
In that case, most common gearing, spur, helical, planetary, will backdrive. In fact, occasionally such gearing is installed backward to get speed increases rather than decreases.
The big exception to the above statement is worm gearing. The general rule that we follow is that a worm gearbox is backdriveable at a ratio of 25/1 or less. Above that ratio, the gearbox simply locks up and, if forced, will break either the shaft or the casing.
You will note in some of the above posts that there are a lot of variables that affect actual field performance---lubrication, temperature, gear tooth finish, vibration, shock loading, etc.
Bottom line, the gearbox manufacturer is going to be your best source for advice on backdriving since it their warranty to protect.
As a student, you will find, as you grow into your chosen field, that the manufacturer is often the first place to turn.
Good luck on your studies.