Disrupt:

Disrupt alters the initial rotation of a particle by adding some user-controlled randomness to the X, Y and Z axes of rotation. Each of the Disrupt value determines the maximum angle that can be added to or subtracted from the particle's rotation for the given axis. So if Disrupt Y is 75, at most 75° will be added to or subtracted from the Y rotation of a given particle.

I've attached some images which explain Disrupt. The generator in these scenes is an XZ SS2 plane. Particles are the arrows, which have their orientation mode set to "Child" (except for the last image). The prototype arrow is pointing in the positive Z direction. The camera is looking down at the scene from the top.

Except for the last image, the only value which changes is Disrupt Y.

Disrupt Y = 0:

In this image, all the arrows point in the same direction. This is because nothing is being added to their Y rotation, as Disrupt Y is set to 0.

Disrupt Y = 15:

There is now some variation in where the arrows are pointing. It isn't huge - the variation between the prototype group and a given arrow is at most 15°.

Disrupt Y = 45, Disrupt Y = 90:

Here, the variation is becoming more and more pronounced.

Disrupt Y = 180:

The initial Y rotation for any particle is now random, since as much as 180° can be added to or subtracted from its Y rotation. Compare this to the image Random Orientation, where not just the Y rotation is random, but all three axes are, resulting in total randomness. Using Disrupt, this randomness is kept under control.