Trail is the horizontal distance between your forks steering axis and the center of the front tire’s contact patch. Setting the trail too long or short can make a huge difference to how your buggy performs and stears
Learn more about trail Wikipedia.
When making a set of forks for a buggy, the rake and trail must be set correctly. The links on this post should help you work out the correct rake and trail for your buggy.
Trail is a function of head angle, fork offset or rake, and wheel size. Their relationship can be described by this formula
Where 
wheel radius, 
is the head angle measured clock-wise from the horizontal and 
is the fork offset or rake. Trail can be increased by increasing the wheel size, decreasing or slackening the head angle, or decreasing the fork rake or offset. Trail decreases as head angle increases (becomes steeper), as fork offset increases, or as wheel diameter decreases.
Try this Trail Calculator