In [Kerbal Space Program][1], they are called **Radial** and **Anti-Radial** on the Nav-Ball.

>**Radial and anti-radial**
>
>These vectors are parallel to the orbital plane, and perpendicular to the prograde vector. The radial (or radial-in) vector points inside the orbit, towards the focus of the orbit, while the anti-radial (or radial-out) vector points outside the orbit, away from the body. Performing a radial burn will rotate the orbit around the craft like spinning a hula hoop with a stick. Radial burns are usually not an efficient way of adjusting one's path - it is generally more effective to use prograde and retrograde burns. The maximum change in angle is always less than 90°; beyond this point the orbit would pass through the center of mass of the orbited body and the ship would traverse a slow spiral in towards the orbited body.
>
> \- [KSP Wiki - Maneuver Node Directions][2]

![KSP Symbol Gallery][3]

  [1]:https://kerbalspaceprogram.com/
  [2]:http://wiki.kerbalspaceprogram.com/wiki/Maneuver_node#Directions
  [3]: https://i.sstatic.net/U5Eoq.png