I believe that means that the collision is not head-on, but somehow sideways. I guess this can be defined more precisely in terms of the objects' centers of mass.
internal oblique opposes the external oblique
Oblique lines:
The artist chose to paint the scene from an oblique angle, capturing the unique perspective of the city skyline.
Oblique means at an angle.
Slanting. A slash (/) is oblique
oblique rectangular
Oblique means slanted or at an angle.
High oblique includes the horizon and low does not.
internal oblique
A Little Oblique was created in 2004.
One's a triangle.
movements in the oblique plane