Usually thar term is used to describe 2 different GM front clips that used to be common to use. A simple rule of thumb I used was that the more the front end comes to a point the more you need a rear steer. A front steer application in many early( almost ALL) cars requires a lot of modification to the area in front of the suspension to eliminate interference with the sheet metal. When you start doing the more "boxy" style later cars it is probably no difference which you use.
Also used in reference to where the steering arms are located on the spindle. This is a major factor in steering rack conversions. For example, the MUST II system is FRONT STEER whereas the TAURUS system is REAR STEER.